Response #32 at the mega-thread referenced:
Altitude vs. Barometric pressure
Eaglet quoted the EXBAL-for-Dummies doc included with the program, and he is right that it was Perry System's intent for you to use altitude. It's a very old school program written before hunters could field access actual pressure information.
But newer versions allowed for use of station pressure, -with altitude always left at zero.
I suspect this is desirable for you.