optimum humidity level

So I'm confused over a very basic newby question: What should your relative humidity level be?
My grow room, aka the spare bedroom, stays about 38 most of the time. I have a room humidifier that brings it up to about 50%, if I'm lucky.
It really seems like it takes forever for my soil to dry out. I don't water in large amounts....just about 1/2 cup every couple of days but even at that, the soil stays sort-of moist.
Am I over-thinking this?
Thanks for any comments.

Veg-40-60%
Flower 40% or lower

Thanks man,
So, as long as I'm showing my ignorance... How many days would be reasonable between waterings? What I mean is...I'm trying to figure out a regimen so the soil has a chance to dry out a bit.
Opinions are appreciated....

Wait until the soil is dry a couple inches down then water until you get runoff out of the bottom of the pot. It should pretty much become a routine in the same environment. For instance, my plants get watered or fed every three days. Good luck.