Since forever now, the biggest reward you get in Cyro is for lagging behind and waiting for the def tick. Rumours have it you can become emp this way.
You will have noticed the yelling "PUSH NOW", "MOVE ON" or whatever! It really means: get away from here, so i can harvest the AP you earned.
Nevertheless, this is no fun playstyle. How to fix it?

TL:DR Those participating in the defense get the AP regardless of their location at the end of the fight (somewhat quoting from the first comment here)

The game knows, apparently
a) at which point fighting starts at a keep or resource (t0)
b) adds up internally any AP for enemies killed from this point on
c) recognizes at which point there is no fighting around a keep or resource anymore (t1), and checks some time if there is really no fighting so we get (t2)
d) evaluates which chars are at t2 around a certain area of the keep or resource and distributes all AP collected equally among them.

So if you are lucky, arrive at a resource after all have moved on before t2 happens, than you get a ton of AP for nothing. And all that fought for the cause but moved on (as they should) get nothing. Great coding, ZOS!
Now /sarkasm off.

It does help a little to reduce the time between t1 and t2, as recently happened, because chances are higher that some fighters are still around.
The problem does not exist with off ticks, so make them more rewarding, as done recently, helps as well.

The real fix, though, is very simple.
You have to add during b) a list of all players involved in fighting at the given spot. The list closes at t1.
(Whenever there is additional fighting, t1 is extended, obviously, that's how it is already now).
At t2, the AP collected are distributed amongst all fighters ON THAT LIST WHEREVER THEY ARE IN CYRODIIL.

This way, late laggers get nothing. All real fighters are duly rewarded. Cyrodiil becomes a dynamic place, finally.
Wasn't that difficult, was it?