I have a 6 bulb sunpower over a IM black 25. Almost exactly your dimensions. With all 6 bulbs on par about 270, about 10 inches down, with fixture ~7 inches off water.
Right now,i runniing 2 radions gen4 xr30 pro sit on top of a 36in tank and i did not like it.I think,there are few corals got some burn tips from the hot spots.I don’t know if the 8 bulbs would overkill for 36l by 24w.Thanks