leaves dry and curling up

I still think it is light based on what you are saying, unless your RH is like 10-30%? The lower buds/leaves doing better is a clear sign usually that it is related to light. Another way to lessen the light stress on your plants is to lessen the amount of light they receive per day if you do not have anymore room to move the light up, shaving off an hour of light per day is very similar in effect to raising the light. Seeing as these are photos and you are most likely on 12/12... going to 11hours of light and 13 hours of dark will lessen the light stress on your plants. Plants can only use so much light, more is not always better, and usually to make the most use out of your light, you need to be supplementing heavy with CO2.