In my experience, a standard stingray on a 20 long is high light(same height as a 10). I run co2 with it even. However, doubling the height on my 29 really cuts the strength back. I’m not even sure I’d call it medium on a 29. I have an additional light on my 29 alongside the stingray.
If you want a good light for a tall tank, I’m not sure you’ll really find many cheap options.