the inner side of the shifting cage is deeper on the triple.
maybe the compact double type, will work better they too lower
the pushing side of the cage, as the chainring sixes are different by radius.

If the chain rubs on the side of the cage its up to you to re center it so it doesn't,
not the mech to do it automatically ..

and yes chainline for a double you have to fit a shorter BB axle,
where the middle ring was,
is to be the center of the space between the 2 chainrings.