I agree with this. When I used to raise shipped CX chicks it was not unusual for me to lose a few in the 1-3 days after they arrived. And, back then, I used a heating lamp and kept the brooder plenty warm.I think you had it on the right setting, but I agree with others here, shipped chicks can need higher temps, especially at first.
I've switched to hatching out my meaties and the level of hardiness is very, very noticeable. They are eating on Day 1, so they haven't depleted their entire stores during a long, cold transit. They are tough little chicks. I've yet to lose a home-hatched chick that hatched normally.
To illustrate, on my last hatch of Red Broiler chicks , I put in them in an outside brooder (an old rabbit hutch) when they were a day old. Nighttime temps in the high 20s. I use a Brinsea brooding plate. First morning when I came out, everyone looked fine, but I could hear one chick making loud distressed peeps. I couldn't find the chick anywhere in the brooder and then realized it had managed to squeeze outside the hutch and was lodged in a small space between the back of the hutch and wooden wall, the hutch was set against. I don't how exactly how long it had been there, but when I retrieved it, it was very cold. I warmed it up, returned it to under the brooding plate and it was fine.
This F*in heater burned the backs of the chicks last night on the higher setting. Ughh. I now have the heater standing up as a space heater and my rent a coop brooder plate in there. Down to 10. If I lose one more I may lose my marriage also, because I am bringing the remaining chicks inside for a week or two.
Sorry you are going through this. It seems like circumstances are conspiring against you. I never really thought about it, because I've grown to love my brooding plates, but maybe for shipped chicks in cold weather, a heating lamp is actually the better option -- at least for the first few days until they've got a few meals in them.
Hang in there.