Here’s the standard I use. If plants are praying and I need more coverage, I raise the light. If they’re praying at a high angle, they’re getting too much. I had some tops yesterday with the leaves pointing almost straight up so I raised the light.
I used your approach when running a 315W CMH in a 4x4. I just keep an exhaust fan running all the time. I don’t worry about humidity most of the time. It probably affects my yield, but the plants are healthy.
One thing about low humidity is fewer pests.