the bigger the pot the bigger the plant,
Agreed. I was thinking that, as soon as I seen the huge amount of wasted space, in those pots. Trust me man, don't try to save a few bucks on soil, fill 'em to the top, because when it's all over it'll pay for itself, ten-fold. If possible, tip the plants upside down and add more soil. If not, add a bunch more on top, and the roots will spread and fill that wasted space. More roots = stronger plant = more yield. It also looks like they are lacking some magnesium, and maybe others(can't tell from the pics), in which case, the extra soil will also help. Are you feeding them? If so, how much, and how often? What NPK ratio?
Otherwise, they look pretty good. A little small for their age, but not too bad, overall. If everything goes smoothly from here, you shouldn't have any problem pulling close to 2 ozs each. Seriously though, more soil will help tremendously.