chicks just like sleeping in a big cuddly pile, but it could be because of the orientation of the light. if you put your hand where they were lying for a little while, how warm does it feel? it should feel hot like the bright sun on a hot summer's day, but not uncomfortable/close to a burning feeling. the other side should be closer to room temperature. if you can get a little traditional type glass thermometer and put it on the hot side that would take a lot of the guesswork out, it should be about 95F.

edit: I'd also suggest a broody plate when you upsize their enclosure. it helps them adjust and regulate temperature much better, promotes proper eye development, and stops them from overeating. I use this one and love it. raised 40 chicks with it last year.