I'm in the process of remodeling my bathroom. I tore out the
solid-surface and drywall that was under it. I'm putting in a
fiberglass shower pan insert. I'm thinking of using felt, backerboard
and then tiling over that.

My question is, the flange of the insert sticks out about 1/3 of an
inch. So, I'd have to use furing strips, correct? However, what about
the transition from the backerboard to the drywall (about 6' up)? The
backboard will be sticking out about 1/3" of an inch. How do I go about
this problem?

Thanks for any advice!