Eh, this is probably what you’re thinking of. And considering that I remember it, I should have looked at it again before I posted. I blame exhaustion. I’ll transcribe the contents of the image for the benefit of easier searching in the future:
One of your opponents will be chosen based on your average ATTACK team rating over time. Defend team rating does not factor into the matchmaking.
The other 2 opponents are chosen based on:
a) A combination of your PvP Ranking & Level
b) A combination of your PvP Tier & Level (I think… not 100% certain on that one, so I’d need to check)
Again, though, those probably aren’t individually linked to the 1, 2, and 3 trophy options. It probably picks 3 opponents, one for each method, and sorts them by team power.
I wonder if there’s something broken in the function that returns your average attack team rating, and that it’s factoring in defend team rating as well – or only defend team rating. It wouldn’t be the first time they got attack and defend teams mixed up. I remember defense teams getting reset to either Team #1, or the last attack team used, or something like that. I wonder if the slot people have their defense teams in is a contributing factor. Might explain why some people say changing their defense team affects their invade options, and others say it makes no difference.