Sanity's Eclipse completely ignores mana loss reductions of any sources: Kaya, Arcane Rune and Arcane Aura with Talent

The spell removes 40% of all hit heroes' mana.

Here you can see how two Weavers, one with 10% mana loss reduction, but otherwise both with the exact same stats lose the same amount of mana. 963-963*0.4=577 mana left. The one with Kaya should have 963-963*0.4*0.9=616 mana left.