Talismans for true damage characters

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?

The formula is (Magic stat + Attack stat) x (modifier) =damage produced. The modifier is a decimal, and from what I gather changes for each character, and it changes based on if the attack was perfect, good, okay, or late for a basic true damage attack. The modifier value for my red pyro soldier is 0.49.
Soulless demon has a modifier based on Max HP, and to my knowledge this modifier (formula), has not been calculated yet by the community. I would suggest if you'd like to figure out the formula, to use a toon without skill shards invested into it. In addition, the attacks need to be UNBUFFED, so be careful with the passives and skills the rest of your team has.

How do I calculate the modifier on my character?
For a basic character this is easy, you'll need a bunch of perfect attacks, unbuffed, on similar creatures (level 1 of the rift), with neutral affinity. Then use the above formula, the characters stats, and the damage produced to fill in the modifier value. Change talismans as you go to change the variables and note any damage increases or decreases.
I have absolutely no idea how max HP scales true damage, but I'm going to guess its the same formula as posted above (attack + magic) x (modifier), and the modifier value changes with Max HP ->this is only a guess.
Good luck and please post results if you are successful in cracking the math.

Defence and MR are additional modifiers for physical and magic attacks. One of these days I'll try do some analysis... No rush though, I think the interesting tradeoff is offensive vs health vs special. Def/mr are vaguely interesting if you can find a level or boss that deals predominantly physical or magic damage.