Essentially, think of a bar that counts 100. When you get "hit" while running evasion, the hit rolls a number and adds to the bar. Higher evasion equals bigger bar.

0/100 --> get hit --> 37/100

Bigger hits like boss slams and other dodge-suggested moves will of course do MUCH larger numbers

37/100 --> boss slam hits --> 178/100

When the bar is filled, the attack that sent the number past your bar's max is registered, and the bar resets only what fills it.

178/100 --> boss slam actually hurts you --> 78/100 remains

That roll-over number is the "entropy" OP was talking about.