Like everyone else said, they look happy.
Trick I recently learned to make roots grow, is to let the medium (in this case coco) dry out as much as absolutely possible without negatively effecting the plants.
I grow roots original soil with few inches of their coco on the top, and in the past have used about 1/4 coco to 3/4 roots original, and only thing I noticed was I had to feed much heaver.
I also grow in
smart pots (someone mentioned them above), and am going to gravitate towards beds, although the areation is nice, it also seems to give a false sense of dry (if that makes sense) and leads me to water a tad bit too early... that and I hear from people they are harder to flush. Reasoning behind being harder to flush according to others is that the water doesn't flow through all the soil and leaches out the side, but the
smart pots I buy from HTG Supply (the cheap ones) don't let water leach through the sides, so this can't be it. I flush a lot harder than many of my friends and am starting to think it has more to do with the material holding salts in the sides, than it does anything else.
I can only speculate that your coco medium might be having a similar effect, causing you to water a tad bit too early, not to the point where it effects their health much, but enough that the roots don't feel the need to 'reach out' for more water.
Anyways they look great, and based on the tid-bits growers I greatly respect have been feeding me, my only recommendation to you, my friend, is to try beds (for dozens of reasons).
Once again, they look nice :)