I can't wait for the official word, but, based on my experiences:
Between 1 and 3 power: shotgunning unfocused does the most damage.
4 power: shotgunning focused does the highest rate of non-bomb damage in the game. SanaeB is the new MarisaB. Shotgunning involves getting all 4 frogs hitting, which requires getting very close to the boss.
Long-range, against bosses, you always want to be focused. It's the same reason Patch-Fire exists for SA MarisaB.
I'm pretty sure SanaeB's normal shots (amulets?) do more damage unfocused. For this reason, killing large fairies should almost always be done unfocused, since large fairies' hitboxes aren't large enough to hit with both focused frogs.
I'll be interested to see who wins out in the end for score runs, SanaeB or MarisaA. SanaeB is better in pretty much every way, but MarisaA's graze hitbox is substantially larger, and piercing's pretty awesome.