Hi, it looks like your using LED but don't see the wattage? I would recommend buying a light meter to measure the LUX to work out the intensity at different heights. they're inexpensive. Plants can still get light burn even without heat.
I have a budget 600w led light and had no problems having the plants just 6-8 inches from the top of the plant but it's not a professional light. They look like they're really trying to stretch so personally I'd half the distance to about 20cm. You could probably get away with lower. It's all up to you though. Good luck with your grow!