It says something for the relationship between Clermont and Leinster fans that it is has survived so amicably to this point.
Consider the reasons for the Auvergnians to spit on the ground every time they see sight of the three-times European champions: four games played between the teams in the last three seasons, and even the solitary win for Clermont came at the high price of handing over a bonus point.
The circumstances behind the stats give more cause for grievance. In the RDS three years ago, they were handed the game, save for Brock James gift-wrapping it to carry home. He dithered and dodged and Leinster reclaimed the package.
A year later, with Stade Marcel Michelin rocking, the same player had the chance of sending Leinster home empty-handed, which would have had a critical effect on the race to qualify. Six minutes left on the clock, Clermont on top, and James hooks his penalty when he needed to hold his nerve.
Top of the list though was last season's endgame in the semi-final in Bordeaux. Wesley Fofana, perhaps the most dynamic centre in European rugby, breaks a tackle to reach and – seemingly – score the try that would finally have seen off Leinster. That's how it looked to pretty much everybody, in real time. Including Leinster scrum coach Greg Feek.
"From where I was sitting I thought it was all over red rover," he says. "Especially the body language from them, you know? And the fact that it was over the line and the ball was over the line. Even when you look at the replay – and then (referee) Wayne Barnes goes . . . (cocks his head to the side). And that movement gives you hope."
We were in New Zealand in June when the draw was made for this season's Heineken Cup. Our first reaction to the sight of Clermont and Leinster in the same pool was that sooner rather than later something would change in this relationship.
It didn't make sense that a team with the satisfaction of back-to-back titles, and a weaker line-up now than when they secured those trophies, could consider themselves favourites against an improving squad who have put this competition at the top of their shopping list.
Last weekend Clermont went to Toulouse with the biggest hitters in their pack not in the starting line-up. Even so they almost managed to take a bonus point. The French Top 14 is lopsided enough to allow clear targeting of games well in advance. If things begin to fall into place then you could arrive at Christmas with either your place in the top flight secure – this is the sole ambition of more than half the teams – or else your progress to the play-offs so firmly on track as to require a dramatic upset to derail it.
Clermont know they are headed for the play-offs in the Top 14 because they have a squad big enough to cope. By Christmas, they want the security of being on the same trajectory in Europe. That probably requires doing something they have yet to achieve against an Irish team: winning the head-to-head.
It's possible they can qualify without achieving that – the collapse of Scarlets increases the chances of Clermont and Leinster making it through – but they will approach this afternoon looking to make a critical down payment.
Their home record is phenomenal, hitting the 50 games unbeaten mark with the win there over Toulon last month. For this afternoon they will have a forward pack that contains the outstanding ball-carrying ability of No 8 Damien Chouly, with the heavyweight front row of Vincent Debaty, Benjamin Kayser and Davit Zirakasvili – all of whom benched against Toulouse last weekend. In between, you have the much-missed Nathan Hines in the second row alongside Jamie Cudmore, for whom the expression hard edge falls well short.
Filling the second row is a real issue for Leinster, where they desperately need a big hitter alongside their leader, Leo Cullen. Hines and Brad Thorn were key figures in the title wins of the last two seasons. It will require something truly extraordinary from Damian Browne to convince Leinster fans that the gap has been successfully filled.
"He's played in the French Top 14," Feek says, by way of introduction. "He's been playing rugby now for 14 years and he's played tighthead lock for that long, and if the track is a bit sticky and things get into the mauling, which they will at some stage, and close-quarter stuff . . . I get the feeling that Brownie has been kind of stereotyped as this (type of play), and that's it.
"I think he wants to prove that he can do more than that as well. The beauty of rugby is you've got the physiques that offer different things and some games they suit. I think we need him this week if he's ready and able."
It will need more though than going toe to toe with Cudmore, who Browne came up against in his days with Brive. The surface in Stade Marcel Michelin should be good enough today, and when the home team get a run on you it's not just hard going, but hard going with tempo.
"Yeah, our pack is okay but we've got to rival what's coming at us," Cudmore says. "We had a little hiccup with that performance against Toulouse – it was one of our worst this season so I think that will help get us right for Sunday. We always play better with a bit of fear in the guts."
Nice thought that. If by the end of the first quarter Chouly is already charging around like a young bull, and Leinster's forwards are going backwards, then Clermont will have started as they wanted.
"He's pretty useful, a talented young fella and gives us a lot of go-forward," says Cudmore of the No 8. "I'd say he has the knack of being in the right place at the right time."
If Browne is under pressure to perform in the second row, then Andrew Goodman is the equivalent behind. A solid utility player, you'd fear Fofana will be in a different league to the Kiwi.
Leinster have won nine from 12 competitive games this season, but between the gap at second row and the loss of Brian O'Driscoll and Rob Kearney, they have never looked like they were on a roll. Fergus McFadden, shifting as usual from wing to centre and back again, has been one of their go-to players.
"Collectively we haven't put a complete performance together, which has been frustrating," he says. "We put a very good 40 against Cardiff before we broke for international duty and then died off early in the second half. Exeter and Llanelli were mixed. Exeter was a bit of a slog-fest and Llanelli was some good in the first half and again we just didn't really play for the full 80.
"It's all about us this week. We know Clermont really well. So does Joe. It's a massive challenge. We know we're underdogs. Historically so far this year they have been playing better rugby and scoring more tries. They've maximum points in Europe so it couldn't be a bigger challenge."
The worrying thing for Joe Schmidt is that his side are sure to rise to the challenge, and likely still to fall short. How far short will determine who tops the pool. If it is dramatic then Leinster fans will feel what their counterparts have been experiencing since this fascinating fixture got going.