There are many many variables that can determine the size of your plants, genetics, pot size, lighting and so on, they don't look stunted to me and they look healthy and thriving to me...Just keep doing what your doing BUT if you feel as though they're stunted or not as big or want to do more, I would increase the intensity of your light if possible, move it closer but your going to have to make sure your DLI is on point as well, RH and temp..You can download VPD buddy to get your parameters