I always recommend TO push thiem all the way back. Reason being, there are a few combinations of bellhousing / flywheel combo's out there. Plus if its a custom built converter YOU need to measure distance between conv mounting and flexplate. If converter has to be pulled more than 3/8 - 1/2 You will catch the problem there instead of breaking the front pump. If converter is pulled too far out the front pump, it is guaranteed to break front pump !!!

Anotther hint, do not use trans bolts to "pull up" the trans to motor surface. If it wont flush up by hand there is a problem
Converter fasteners may be bolts or studs, depending on manufacturer