maybe its like the dmz PS method, when they pump more power in it the middle of the beams, where they collide will make a ball, eg vegeta vs goku gohan vs cell, buu vs. heck its almost always the ball kinda power struggles in dbz
would be cool though, i liked DMZ style of Power Strugling, only it wasnt bug free, that was the only downfall to it
the beams would grwe bigger, and when someone was out of ki it would explode, or the powerlevel must be much higher then you opponents