day 52 only half the clutch is dented?

Hi I have a clutch of 4 and the two eggs at the back of the egg tub have been dented for a couple of weeks or more but the two at the front are still perfectly round, shouldn't they be denting by now? the heater is at the back of the inc so it makes sense the back went first I spose.would think they would be dented by now though wouldn't you?

Charlotte

Occasionally they don't.

The six clutches I have hatched so far this year all stayed plump. They are on the humid side though. It won't hurt.