They won't, and setting up enough for 100 chicks would be very difficult. You're better off using heat lamps.
Why so many birds?
Meaties or layers?
What is your climate?
Geez, Sorry, musta missed the size.
Flat will give you room for more chicks.
Adjustable legs will give better management as they grow.
Remember they need to touch their backs to the pad.
Plain cardboard top and smaller mesh support will mean less trappings.
I dinked around with a couple...
It took a lot of researching to find a rack that would work....I wanted to avoid 'bunching'.
The mini bungies I got at a hardware store.
Cut in to the heating pad?!
Don't do that, very dangerous.
Put the other plate at the same height and right next to the MHP, they'll want to stay together.
12x24 worked for 16 here...but it wasn't draped.
....or something disposable, like the cardboard I used.
How big is it?
You don't measure the floor temp with a plate/pad/MHP.
The surface of the plate, where they touch their backs, should be from 100-120°F.
Measure it with a infrared temp gauge.
6 might be OK, 12 would be crowded.
They need to have easy access in and out from under there.
That's why a flat plate/pad, with all 4 sides open to egress, can work better than a 'cave'.
Sorry, forgot to punctuate properly.
Might get too hot in there, most folks using a pad/plate don't measure air temp like that.
Good thing you can turn it down.
How many chicks will you keep in there?
As long as they can't get their heads stuck in it.
BTDT.
I found having the pad underneath the wire rack is best.
Went thru several iterations before finding a good design:
https://www.backyardchickens.com/articles/pseudo-brooder-heater-plate.67729/