hmm, i thought topping was the process in which you cut off the top (not FIM) and it split into 2 or more colas? if so, i dont see what you mean by increasing light penetration without also incorporating lst in some fashion (in fact, i would say without the lst you would lose light pen). are you sure you are not referring to supercropping?
as far as i know, 'topping' will just about always increase your yield in some sort of manner, small or large. its when you top to the point of having 6 colas that you start losing yield (hormones are split between too many budsites, resulting in multiple undergrown colas).
i could be wrong, just throwing that out there.