Another thing you could do for your 20 gallon for temps aren’t high enough on the cool end, is to just shift the lamp a touch closer to the centre. This should increase your temps on the cool end, it’ll shift your hotspot to the cooler end a little but that should’ve be an issue.
Your 50 gallon sounds good. And you can have cool side temps as low as 75.
Ideal humidity for a bp is 60-65%. So having it at 70% would totally be okay. It’s better to be a little higher than a little lower. I’d say 50% is quite low. It isn’t terrible, but it’s not a good spot for shedding time.
I love using UTH because they’re getting belly heat while being able to remain under their hide, but you definitely can do heat bulbs instead. I have trouble with humidity which is why I use a UTH as well, and use an 60W heat bulb as ambient during the winter and fall seasons.
I checked the temperatures when I got home last night and it looks like the 75w w/thermostats are keeping things in check perfectly! I did not know that about the humidity! I always thought it was 50%. The more you know!! Thank you for your help!