It will depend a little on enemy composition, but often I've found in dungeons that there's one enemy of the pack that tends to have more HP than the rest.

In those cases, I use the single-target Kasha and Gekko combos to keep up my damage and speed boosts then only use the two sens to cast Tenka Goken. If I have extra kenki, then I spend that on Kyuten. If, however, there is not that one enemy to apply a little more focus on, then you'll use your two AOE combos still with Tenka Goken.

I haven't done the math, but at a casual glance, you probably want to switch back to single target moves at 3 enemies remaining. Though someone can correct me if that's not correct.