is what i do is lay the holster cutout flat and place the support piece on top, making it fit exactly to the flat holster. (no conpensation for the bend) then i glue and sew it. once that is done i fold it over and glue and sew the holster together. it will feel hard to fold because the support piece wants to force the holster back open due to the lack of trying to compensate for the bend with the suppoort piece. but this is the purpose of the support piece, to keep the holster from wanting to collapse when drawing the gun. i have not had any problems with bunching at the fold this way.
Tony