I have 3 tents. The other tents have AC Infinity and HLG lights. I also have a few older ViparSpectra lights as spares in case of a failure. I also have a new Phlizon light that I haven't been able to use yet. I'm hoping to have that going this fall season when the weather cools and after I clear a space for it.
If it works for you, that's great, but I thought you were questioning whether the XS2500 was adequate. I looked at the specifications again and realized I was incorrectly remembering the focusing capabilities of the light. So, yes, that light should work well for your style of growing. Sorry about my poor memory.
Without measuring, I'd guess about 24 inches. I'll increase that distance before changing to flowering to account for stretching. It doesn't look like these White Widows (photos) will stretch much, though. They were stunted due to a soil pH problem. I plan to veg them longer than usual.
Generally speaking, the greater the distance the greater the spread, but
the inverse square law is a matter worth considering. Do you measure the light levels at different places in the tent?
I don't recall that I have ever run any light at full power. My XS2500 is currently pulling 103 watts at the plug, which is 41%. The taller plant is showing slight light stress on the top leaves. I doubt I could run a full 250 watts at 12 inches without frying the plants, but, like I mentioned, my style of growing is different from yours. I did run the light at close to full power the last time I flowered with it.