I can only speak on the Lines. Those I would go dead center or -2. My Bacons are dead center and I love it that way... I would say it's more of a personal preference when you're talking about a more quiver-like ski. If you're on the fence with the the Opus, I'd go -2.
With the yle in the 187 its not truly symmetrical even though when you look at the sidecut numbers. You get some nose dive when mounting recommended though. I bought my yles as demos and the demo binding was mounted at recommended but I put my own bindings on and had mounting issues trying to put on my bindings and ended up 2cm back from recommended and they skied much better. Still ski switch just fine at 2cm back too.