Ceramic Heater Over Undercage Heater?

Had a freak out yesterday when I checked the temperature of my boa's warm side and saw that the under tank heater was still not warming up the cage. Eventually I settled on a ceramic heater since my boa seems to like being on his tree more than his hide. I've yet to see him actually go into it and sleep, though I have seen him slither through it to get to his tree. The girl at the pet shop told me that keeping the under tank heater on and adding the ceramic heater would be fine. I'm afraid it will be too much heat. I also bought a digital thermometer with probe to keep on the warm side where I placed the ceramic heater and so far the temps are good. So, should I keep both or remove the under tank heater?

Since I've bought the ceramic heat emitter and also added a thermostat that both the undertank heater and ceramic heat emitter are plugged into, I still haven't had success in raising the temps to the right levels on the warm side. I've also read that cardboard cover helps retain heat but that's not helping either.

I need some help, what else can I do?

Can you post a picture of the cage and how you have it set up?
What wattage Ceramic Heat Emitter have you got and what are the temperatures it is producing?

I will as soon as I get off, which isn't too far off.
It's a 60W, so far it's put out 93 degrees right underneath it, which is fine for the basking spot. The rest of the warm side is at about 83. It's a 20gal tank, with the 10-20gal undertank heater underneath that half.

Your temps are fine. What are you trying to reach?

The care sheets/graphs I've read say cool side is supposed to be low 80's, warm side high 80's (85^) and basking temp in low 90's.
It's good to hear they're ok then, I was shooting for perfect.

From our caresheet.

The warm end of the enclosure should be around 85 Fahrenheit (29ºC), with a basking area of 92 Fahrenheit (33ºC). The cooler side should be in the low 80s Fahrenheit (26-28ºC)

I assume that it is an aquarium with a screen top? If so covering a large amount of the screen should also raise the temperatures a bit.

Your assumption is correct. We have covered a good portion of the screen.
Here are pics of the cage...sorry if quality isn't good, had to upload from phone.

Closing off more of the screen top will help you retain heat bettter. I would just get a peice of plywood the size of the top and then cut a hole in it for your light reflector.

What about plexiglass, would that be ok to cover the top?