Sleeping outside of heat source

[Judechicks]

We have 18 baby chicks, 11 days old. We are using a mama heating pad setup. They are inside in a nice brooder, see pic below.
My question is, for the last few days they have all huddled together to sleep outside the heating pad cave. They are all eating, pooping, drinking and cheeping quietly. Nobody seems unhealthy, in fact they are all feathering out beautifully. It is typically 20-22 degrees C (Canadian) inside.
I have researched like crazy and it is driving me nuts that they are not sleeping in their cave. Should I be worried?
New chick mom

 

[igorsMistress]

It could be that the cave is too small for them to all fit comfortably under it. Can you raise it to give them more room? Or it may be too warm underneath it.

 

[Peppercorngal]

I believe that the cave is now too warm for them to feel comfortable. Chicks will pile together to sleep just for companionship, it's usually not because they are cold.

 

[rosemarythyme]

As long as they know where the heat source is, I let them decide if they want to use it or not. If they're comfortable without it, no reason for them to sleep under there if they don't want to.