It's not exactly a "Miss". It "Hits" but does not connect and you don't get damage. You'll know if you have PD [Perfect Dodge] by the little talk bubble that says "Lucky!".
It dodges every physical attack and is expressed with %. PD is the number next to flee.
So, 111 +10. The 10 is the % of physical attacks you can evade. <- From what I've been told.
Flee & Perfect Dodge does not stack... since they're two different things. Flee shows "Miss" while PD shows "Lucky!".
It's a lovely thing really. Just hard to get very good with. Fortune daggers seem to help much, + 20 PD & +5 Luk. <3 PD.
Hope that helped somewhat.
Edit: Critical = physical = Possible to evade with Perfect Dodge.