So glad so many new members are finding us, and dues are being paid in the form of all of the photos!! Welcome to the Broody Brigade, @Ahavati .! And welcome to others I may have missed as well!
My feeling is that you really don't need heat under the pad as well as on top of it. The idea isn't to heat the space, It's to let the chicks regulate the heat themselves by using the pad at their backs,like Mama Hen does. We're trying to warm them, not bake them. But if it's working for you, then I don't see any reason to change it. My only concern would be that they'd overheat, move away from the "cave" and then be hesitant to go back in, which might lead to them huddling in a corner somewhere, chilled and even dangerously uncomfortable. Of course, I assume that it's warmer where you are than up here in Northwestern Wyoming, so that might not be as risky an issue as it here.
I guess that reply applies to @AutumnHens as well. As @junebuggena said (and why didn't that @ thingy work?) the idea is to heat them from above. Personally I don't care for swimming pools as a brooder but many folks have used them very successfully. The pesky little buggers don't stay little for long and the sides of the pool are low enough to allow for escapees. For that reason I opt for a wire pen, and I also prefer it because they aren't restricted to just seeing what's overhead....they can see through the wires and get to know their entire environment. The people taking care of them aren't some tall monsters approaching from above. They can see you the minute you enter the area where their brooder is and it takes them almost zero time to see if you have a treat or two in your hands! That encourages curiosity and decreases fear.
But again, if it's working for you, then keep right on doing on it!! You're there, I'm here, and you know what's best for you and your situation!
Reptile pads come up here from time to time. I don't know that we've ever had a clear consensus on their use, but if I'm wrong I know that someone will point that out and steer us to the page where it was discussed. (Sometimes this thread just flies by and it's hard to remember from one page to the next.) Once we start relying on heating from the bottom with other than a heating pad, then the setup isn't really a Mama Heating Pad but just a heat source.
As for power outages, @henless found a pad that not only stays on, but will turn itself back on to the last set temperature in the event of an outage. Here's a link to that pad:
http://www.sunbeam.com/pain-relief/...ology-blue/000771-810-000.html#sz=12&start=18