Welcome to the bp community! All your work looks good and it sounds like you did your homework! Couple of things , IMO, change that housing for you che to a closed housing and that will center and aim more of the heat into your setup. Purchase a "versa top " for a 20 gallon tank. Just make the appropriate air holes into the plastic cover to the v.t. That will also boost your humidity percentage. Stay in peace and not pieces.