Kevin,
Quite possibly the problem is HP5+ and not the Pyrocat-HD. It is a known medium to low contrast film that has a difficult time responding to increase in development that translates into increased density. There are other films out there that do a better job of "pushing" the exposure range. EFKE is one that I would recommend. It is available from J&C Photography. Maybe Sandy King will weigh in on this.

lee\c