Internal Struggle not working with actual Current Health

I have a Diabolic Commander Nether Creature using Darkness Surrounding, It’s own Health boost, and the Diabolic Link (40% shared HP between Diabolic’s), and Ruby Attunement (All creatures have +100% health). For a Max HP of 8million
I then use Internal Struggle to cast a high HP-potency spell, and it should take 25% of the current HP but it consistently only takes 500k out of the current max HP of 8 million!

I am using Diabolic Protection With Nature mage’s +3 bonus “Per class” perk.
SO i have 9 total Diabolic’s, for a 45% damage reduction. Not sure if this effects these other traits and how much Health they drain to use.