I've been sailing for over 50 years and I just learned something I never
realized until I seen it with my own eyes. on the free footed sail. When
turning upwind and you tighten the vang, to flatten the main. The lower
part of the sail becomes rounder. (Due to the bend in the boom) n
outhaul adjustment is necessary.

Maybe I'm missing something with your post but when you turn upwind you
should be trimming hard with the mainsheet and the vang should have no effect.
I would also think if your hauling in harder with the vang than the mainsheet
that's the reason why your boom is bending which is something that shouldn't
happen.
S/V Express 30 "Ringmaster"
Trains are a winter sport