Well first thing I don't like is that light laying down beside the cups. Your cups are clear and very thin, you could be drying out the roots and getting the soil too warm even though the top seems moist.
Second is the top light. You need to move those girls right under the light. Unless you moved them for the pic the plant seems to be stretching away from it. If you need temp control go and buy a cheap small space heater with a thermostat, in Canada I can buy one for less the 20$. You want the girls to be praying to the light, begging for more. They seems to be stretching away for some reason.
Also I used a 12" fan about 4' away on setting one, with it oscillating and my plants loved it, it's only 6 inches tall, but bushy and a nice very strong thick stem.
I'm. Not sure if that clip fan is doing it for you.
This is just a few things I can think of to restrict growth.