They should be just fine. Did you see the first post in the Mama Heating Pad thread? It really gives thorough breakdown on the entire system - not that a heating pad, a wire frame, a towel and a box of new chicks requires much engineering. Yours could well be a little stressed from shipping - I'd be very surprised if they weren't. That sure would make them cling to the security of having the feeling that they are warm and safe under Mama, and just like under a real broody they'll tend to stick tight at first. But curiosity will make them come out to check out their surroundings. Making sure they know where food and water is located is always a good idea, and making sure they know what to do with it is essential. You've done that. There may even be a chick or two that just plain fails to thrive, and that can happen no matter how they are brooded - under a hen, a heat lamp, or Mama Heating Pad. Sometimes shipping stress appears a few days after they get to their new home. Once they know how to eat and drink, you may need to shove a couple of them under there, holding your hand in front of the entrance for a minute or two until you hear this soft, contented churtling sound coming from there. (I know "churtling" isn't a real word, but since it describes that sound so well it should be!) Then you can take your hand away and let them out. After that they will start running in and out on their own.
When I did a temperature check under MHP, the thermometer read 82.9 in a 69 degree room. Most people who have taken temperature readings under there have reported the same, within just a degree or two. If your pad is 6 inches in the front and 4 inches in the back, is there a way you can smoosh it down so the heating pad is touching or almost touching their backs at the rear of the cave? On page 4 of the Mama Heating Pad thread is a video of what you can expect to see. The lights start out dark, and you can barely hear a little of that churtling. Ignore Ken's grandfather clock ticking and chiming. Once I turn the light on they come running out. Let your chicks explore this big world they are now part of. It's all new right now, but within hours they know where the heat is, where they can dive under Mama if they get chilled or scared, and by tomorrow they will even be climbing on top and napping or tussling.
This is the link to page 4, where the video of my chicks under MHP can be found. Remember, it starts out dark.
Edited by Blooie - 9/25/15 at 4:49pm