I have to admit that I don't get why the big chainring / highest gear combo is used for setting the angle of the FD. Is that supposed to be the straightest alignment of the cage so you have leeway on the left and right sides? Why wouldn't it be straighter to put in on, say, the middle chainring and in the middle gear (say 4th, on a 7-speed bike) and align it that way?

I have a 7-speed bike whose FD I adjusted, but I'm still having problems. When the chain is on the middle chainring, I get rubbing on the inside of the FD cage when the bike is in 1st and 2nd gear. When it's in 6th and 7th, I get rubbing on the outside of the FD cage.

Does this mean my chainrings are out of true?