Just make every character that enters combat has AP dependant on sequence.So with max possible 31 sequence (with 10 PE, Kamikaze and x3 Earlier Sequence) player will have full AP (but not more than he had before the combat had started), and with least possible 2 sequence (with 1 PE) he'll have 0% of his AP at start.He again shoots you for 6 AP. He has max possible sequence. so he'll have full 10 AP - 6 for shot = 4 AP. It'll work like it's now works for everyone else.
This whole problem of not knowing the enemy's intentions might just disappear on its own if certain things take place: combat doesn't rely so much on the first hit or players can certainly recognize friends and foes. Other solution would be more advanced animations due to incoming 3d models.
Isn't it obvious that you should see whether someone is holding his gun in relaxed position or pressing the barrel on your forehead?