I run a
sun system boss 315 in a 3x3. One of my favorites, runs real cool, so your ladies won't mind it close.
I keep it at 20" from canopy throughout veg, move it to 18" at the 12/12 flip and by week 4 of flower I have it as close to 12"-14" from canopy depending on strain, your plants will start telling you if you're too close.
No problems yielding a lb of top shelf sticky utilizing a 315 in a 3x3 space.