Any suggestions?

It might just be the phenotype. But if all your plants have very tight node spacing, you might want to slightly reduce the light intensity. I saw that you’re using the Viparspectra P1000, although I’m not exactly sure how many watts it puts out. During this stage of growth, I usually run around 35 to 50 watts with about 50 cm (20 inches) distance from the top of the plant. I wouldn’t recommend defoliating just yet – the plant is still too young for that.