As I understand the basics (absent special instructions based on Max HP or special):

You have a warrior, it deals out physical damage. Thus, you want to enhance the attack stat, perhaps with a set of burning talismans (fierce).

You have a magus, it deals out magical damage. Thus, you want to enhance the magic stat, perhaps with a set of paladin talismans (power).

What then would you use to enhance true damage? I assume (perhaps incorrectly) that enhancing attack magic or special stats do not correspond with increasing true damage. If this is correct how then do you enhance this sort of damage, and if this is incorrect what is the proper way to enhance true damage?