Do your chickens that are panting have shade or are they in the sun?
As long as it's not over 100, I haven't had a problem with my chickens handling the heat. Mine handle the 90s fine, even with high humidity. I don't see them panting. They always have lots of water and lots of shade. They can walk in their outdoor water bowls if they want to, although I don't see them do that, usually.
I think large areas of shade are a little cooler than tiny areas of shade, too. Our areas of shade are from the trees or a building, so maybe that is blocking more of the heat and providing a cooler shade, than something like a thin tarp. I'm not sure. Whatever the reason, it works for them.
I loved the drier heat in Texas, but once it starts getting above your body temperature, even dry heat gets bad in a hurry. I don't envy the people living where the summers are that hot! I remember being totally wilted when it was 114 degrees. I didn't have ac. I used to lay in the bath tub in water that was straight out of the cold water faucet. It was warm, too, but not as hot as the air. We gals of Irish descent need colder weather!