You could probably raise the frame and/or lower the heat. I'd put it down to 3 or 4 and I'll bet they'd be fine. If they start that loud "Doggone it, I'm cold" cheeping and huddling up together just pop it back up to 4 or 5, depending on what you turned it down to. Actually by 4 weeks mine was on 1 for a few days and then off, and they did just fine. So let the chicks call it for you. When I had mine outside it was the time of year that temps outside were gradually going up. This time of year they are going down, so you'll want them acclimated to cold temps pretty soon. Great job!
Sounds great! Thank you for all the advice and support.