Get a bigger light? (sorry... I couldn't help it!)
Well I've never flowered under a hps250, but in that case, the shorter the plants/flatter than canopy, the better.
So if you go for the gallon pots, one thing you could try is bending them over on their sides, or even a nice SCROG, to flatten the canopy and maximize the amount of plant matter exposed to the light.
stinkyattic Reviewed by stinkyattic on . SOG Pots.... Are 1 gallon pots big enough for a SOG style plant grow? Rating: 5