24% is cap... It's accurate! You could try Epiphany affix to increase though. 24%x(1+(3x5%) = 27.6%
Vs Eternal Flawless trophy Defense Affix can reduce your critical strike chance down to 9%. [Max 15% Defense]
Vs build with Epiphany and max critic chance = 27.6%-15% or 12.6% vs 9%...
I think you might be confused with Defense Affix vs AR Pierce on Bloodless Trophy.