As others have said, chain rub on the FD cage is fairly common when riding crossed over (big/big, or sml/sml). To avoid the problem, Campy FDs don't index and the rider can trim the cage according to the angle the chain comes from. Later Shimano added a trip click to their FD lever, moving the cage inboard a bit.

There are those who say never ride crossed over, but that makes no sense. While riding crossed over isn't as efficient as inline combinations, there are situations where it makes sense. Imagine you're cruising along on the ring when you come to a grade. As it gets steeper you'll shift the rear step by step, and at some point shift the front and continue.

But what if you're near the top of the climb and only need a bit lower gear to crest it. You could shift the front (under load?) and upshift the rear, or you could simply shift the rear one more step, ride it for a short while, then begin the upshifts when you crest. Seriously, which do you think is more efficient?

If you don't have a trim feature in your left lever, adjust the FD big gear trim to the barest minimum that allows a crisp shift and clears the outside of the chain in high. That will give you the most inboard range.