Interesting - I've almost posted the same thing. I have four 3.5 gallon Air Pots with Coco Coir and I'm at the 5-week mark. I'm supposedly growing Sour Diesel, but these plants look nothing like sativas and everything like indicas. Fat thick leaves, short and bushy. They would be taller, but I topped them at the 5th node, then the 7th, then more-or-less the 9th. FIM'd one and it's REALLY bushy now, but I lopped a couple of branches sticking up after that as well.
I've never grown in coco before, and this kind of freaks me out. Never seen plants like them before. I'm wanting them to spread wide at this point as they've hit the first trellis net. But if they simply double in height at this point I'm going to be short on space to the light.
As for light - you simply need a PAR meter. Nothing else will really do, but least of all reading power/distance charts and measuring with a ruler, especially with a dimmer. I have a 4x4x7 tent, and I have about 18 inches above the light, which is recommended for heat control with my light. (
HLG-600r). I could kick myself for not having bought an 8 foot high tent instead.
Last crop (soil) I let veg for a long time (over 3 months, but slow growth at start of that), and once the stretch happened I ran out of space quickly. But with a PAR meter and a dimmer switch I was able to keep the light from burning the buds. Just didn't get the even side-to-side coverage I would have had with more spacing.
I think some of this odd-looking density is due to the leaves being huge for size of plant.
I wonder if you also see wet spots on the top of leaves that were underneath upper leaves and touching?