There are folks that will tell you to cull it down to one plant, as it will fill up the same space anyway. In terms of sheer volume, that is correct. However, my guess is you feel attached to the 3 plants which you want to keep, which in my mind justifies keeping them.
To some extent, intuition must guide us, and if you want to keep 3 plants, don’t let them tell you not to. However, I am drunk and high, so I perhaps feel extra strong about what I happen to be talking about.
At this point, you should just keep all 3 pruned back like little bonsais. Treat them like a triple yin/yang in the tent. Yin, Yang, and Yung, which is arguably the third element in this “trichotomy,” LOL.
As for the height of the light above your plants, feel it out. My kneejerk reaction is 18 inches with the LED you describe. Others will say I am wrong, and they may be right. My approach is to eyeball it, then move it further away as it seems necessary.
Stupid is as stupid does? Yes.