My two easy fixes, add more holes, and get a smaller dish. I use the little ceramic souffle dishes for my youngins. Only the adults get the big bowels to help keep the humidity up in the big tubs. Also, if any sunlight hits your tubs that will make the humidity go crazy and raise the temps of course. It took me a bit to realize that even the indirect sunlight (bouncing off the neighbors garage and through my thin curtain) was enough to raise the humidity in the two tubs it hit. That made me crazy till I figured it out

As for the holes, you can always cover them up if the humidity ever drops too low. So don't worry about adding too many.