For daytime temps in New Mexico I would think you certainly right, what are the nighttime temps or are they sheltered enough to not matter?
For example here we are forecast to be in the 50s and maybe even some 60s next week BUT our average last frost is May 15th meaning nights can frequently drop into the 20s right through April it was 5degrees one morning just this week.
If dropping below freezing I would expect 4 week old egg breeds to appreciate some heat yet at that age and think their size would mean very few would fit under a 12" plate then.
The weather here in NM has been crazy. It's been in the 70's last couple weeks and now we are getting snow this week it can be all 4 seasons in one week here. Average is about 60-65 daytime and 30's at night.
We just built a 10x12 insulated shed with a 30' enclosed run for the chicks. They should be just fine here in a few weeks to go out there. We are still completing the shed otherwise I would just brood them directly out there.