That is so interesting! I actually have a conundrum on the opposite side of yours. I have a heat plate as well. Much smaller size, but I only have 11 chicks. 4 days old.
I heard that between 95-105 is good in a brooder, so I tested it several times before the chicks came, by setting a temp gauge on the ground at various heights under it. It’s now fully heated (took about 2-3 hours to get to max temp), and it was at about 105 degrees at the height I set it at. I wanted it to be pretty warm when they first arrived because I knew they would need the extra warmth, after being shipped. They took to it perfectly, all perked up & started eating & drinking. Then I raised the plate, so it was around 95 on the ground & probably warmer higher up (and it does have a feather skirt, so it keeps the heat in pretty well).
Then tonight, when my husband turned off the light in the room, most of them were under the heat plate. When I went back in, about an hour later, all of them were in the opposite corner from the heat plate, all cuddled up to each other. It’s about 78 degrees in the room.
I don’t understand why they wouldn’t be under the heat plate, at 95 degrees on the ground. They instead chose to huddle in a corner together, at less than 80 degrees.
I put them all back under the heat plate again, just to make sure they know it’s there, especially since they mostly like drinking from the water dish from inside of the water dish. 

 Wanna make sure if they get wet, they dry off & don’t get themselves chilled.
This is confusing to me. Because we’re told that you need to pay attention to their behavior… that when your chicks are huddling under the heat, they’re not warm enough. And when they’re trying to get away from the heat, it’s too warm for them. What if they are huddling away from the heat?
Could it be they got accustomed to lower temps when they were on their mail journey here, and now 95 degrees is too warm for them?
I’d appreciate any thoughts or experience on this.