AP trick problem!! please help

Well i have this problem with the ap trick im assuming most people know this trick the ap to overdrive don tonberry or king cautar thing. Well im kind of confused cause the trick is suppose to be what damage you take is how much ap u get at the end right??? well at first it was working cactuar king did 11 of the 99999 neddles and tidus got over 1 million ap i juss keep doin it and doin it then all of a sudden im not getting full ap ne more like he did 5 99999 needles and i got 130000 ap i was like wtf i dunno what the problem is checked everything all 3 characters have ap to over drive all have on comrade overdrive dunno whats wrong can ne one help???

You may have become stronger. Comrade does less as you get stronger, because 9999 damage is more devastating to a person with 300HP, than to a person with 70000HP. So you should go for the HP spheres last, or you could customise a weapon with Overdrive -> AP, Double Overdrive, Triple Overdrive, and Triple AP for maximum experience.