I actually have some HLG 260's. Rspecs, and 3000k V1's. They are some strong lights man. At first I treated them similar to my cmh lights, but soon learned that the QB's on full power are way stronger. So I ran them around 24" the first time. Then I tried them higher, around 36" and still got great results. This round I've turned them down to 90 watts per board, so each 260 is getting 180 watts, and am keeping them around 24" above the canopy.
But that's for mature plants. For seedlings I would start the light super high, like at least 36". Personally, I would raise it to more like 48"+ though at this stage. Then slowly lower it as they adjust.
Also, ditch those domes.