Temerity not granting enough barrier

I found a perfect 80% temerity and thought I’d try a new approach with my druid. He has 80k life and has 3/3 in Circle of Life, so his landslide is healing him for thousands of life per cast. However, even after wailing on stunned opponents so that I know my character is taking 0 damage, I’ll look at my barrier and only have like ~3k. If I chug all of my potions in a row, I can get the barrier up to like 40k, but I should be able to regularly get a barrier of ~64k.