How does Improved Evasion work?

[Ravingdork]

Am I understanding the text for Evasion and Improved Evasion correctly?

If I roll a...
...critical failure, I take full damage (rather than double damage).
...failure, I take half damage (rather than full damage).
...success, I take no damage (rather than half damage).
...critical success, I take no damage (same as before).

[Themetricsystem]

On a success on ANY Reflex Save you treat it as a Crit success.

On a Crit fail you treat it as a normal failure.

When you ROLL a failure on ANY Reflex Save vs some damaging effect you take half of the listed normal damage.

As for what happens when you Crit fail a Reflex Save I'm not super confident if you'd take the normal failure consequences, or if the half damage function would then kick in and effectively turn the Crit fail into a success. Can of worms and all relating to how strictly we are supposed to interpret "roll" in mechanical expressions versus determined results.

[Jared Walter 356]

Ravingdork has it correct.

They addressed this somewhat in the errata. The "when you roll a" result doesn't stack with the effect "changes a result"

Rolling a critical fail you would get the normal failure result. The normal failure result isn't further modified, because you didn't "roll a failure"

The only corner cases I am aware of are assurance and incapacitation.

For reference here is the full errata text:

Changes to the Greater Juggernaut, Greater Resolve, Improved Evasion, and Third Path to Perfection class features

All three of these abilities grant a two-tier benefit on a failed saving throw of the specified type, but (as always) no ability will ever change your degree of success by more than one step. To clarify, we’re making the following clarification to all three abilities. Change the beginning of the last sentence from “When you fail” a given saving throw to “When you roll a failure on” a giving saving throw.