FD chainrub has long been an issue on upgrades, etc.
I have one that rubs when I cross-chain, and only then, so I let it be.
I use it as a reminder to shift, and set it not to rub on the gears I use 99.9% of the time.

Some experts even bend the cage a bit.
I've done that on braze-on FD's, no problems.
Generally, you're talking 1-2mm. Any more, I'd start back at scratch.