Honestly RHPs are great for Melamine or PVC style cages that actually hold the heat that they throw off, but on a glass tank those panels would really be inefficient. And without a solid top, you're going to be constantly allowing the heat to escape...again overworking the heat panel. Just not the best choice for this application... I don't know about you, but I choose my heat sources do to the application and their efficiency.
I know what Melanie meant was that, the UTH is a better choice to use than a heat lamp because they aren't going to sap the humidity out of the air.
OP, if you're having problems keeping the temperatures correct in the glass tank, my guess is that it's much too large, or that your UTH is much too small. Instead of worrying about getting that hot spot just right, maybe you could go with two areas of flexwatt heat tape, or an additional UTH on the cool side...run the cool side area your 82-85 and then your hot side heat tape at 90-94. This will help to bring up the all around ambient temperature.
And this time of year, depending on room temps the cage is in, and the poor insulation of the aquarium standalone, it might be wise to tape some foam insulation to the sides and back of the aquarium. It may be unsightly, but it should help to hold those temps more stable.
Hope this helps.