Does anyone know the formula to add bonus HP per hit die/level?

[Mathias]

4) This:
~ If we're disabled, do nothing
doneif (tagis[Helper.FtDisable] <> 0)

Will never change anything, because Helper.FtDisable will never exist outside of a feat, so this test will always find that it is not there, and therefore nothing will change because of that line. The next two sections are critical - that's where it actually adds the HP bonus to the character.