I get it...though that looks like plenty of natural light to me.
Should be just fine....wouldn't be any different than the Ecoglow brooder with the hard plastic top on it that the chicks press up against. At least the heating pad is soft and cushy. I put mine up under the wire also, as I wanted the chicks to have direct contact with the heat source without the hardness of the wire getting in the way. Your chicks look very contented.
Your right bee. I have a Premier heat plate that I used the first year I got chicks. It's nice and hard and metal. No cushion at all.