If a sa'angreal is a pool of additive power how can lacking a buffer and the ability to overdraw as Egwene did even exist? She seemingly took in a vastly larger amount of saidar than she previously held and that makes little sense if the devices hold a fixed amount of additive power.

Perhaps the buffers are the actual key here. Perhaps the buffers limit an individual based on their potential, only allowing a fixed additive amount that the individual can manage (thus explaining Verin's quote about the CK). This would allow for Elayne to use the turtle to become 2x Nynaeve, but Nynaeve's higher potential would give her access to higher additive potential because the buffer would naturally limit Elayne more? Problem here is the very weak angreal such as Cadsuane and Graendal possess don't make sense since they wouldn't need buffers at all given how little power they access. Or the very strong angreal that clearly show that Egwene/Vora level can match Taim/Sakarnen. Vastly more power than any angreal would add to any individual.

Perhaps Sidious is correct and we'll just have to file this under "nerd dissatisfaction"