impressive, nice sativa you got there.
i myself havent topped many plants, theres also a technique called FIM. that can result in multi tops instead of two or three.
this can also depend on your strain, some strain can not be FIM at all, it can result in mad stress and inturn cause the dreaded herm's
i also read in a few mags and done by mistake, that bending the main stem can promote under growth.
also i see the four corners have no flourcents, cool white ones will make great supplement lighting,
and the leafs can grow up against them and not be burned.
overall i say job well done and keep up the good work.