Hi Joe, it's difficult to really get across my issue but it has to do with the shape and placement of the upper curves and forearm contour (incidentally, I have the same problem with Status basses; P Basses nag, but nothing like as badly).
Because of my neck & shoulder problems I can't float my right arm and have to rest it against the upper bout. On a Jazz it seems that the forward position and height of the highest point, combined with that severe forearm contour, is just a terrible mix for my nerve pain. A P Bass upper bout high point sits further back so doesn't affect me as badly. My Rickenbackers, which are low at the point the Jazz is high and only rise right at the back of the bass, are fine. Historically I didn't have any problem with my big-bodied Alembic Triple O either.
Whether the bass itself sits forward or back doesn't seem to be an issue; my Rics sit further out than a Fender. I think the body being more out of the way sounds positive. I seem to be ok where I can rest my entire arm (like with my T.O.; sadly weight was the issue there) or conversely where the upper bout is relatively small and doesn't get in the way.
