Temperatures are not to be guessed at, you need to know what the temps are especially if your using a UTH.
Dimmers only work well in a temperature regulated room, otherwise they are useless.
Thermostats are a must for uth's as is having a good probed thermometer.
Without a probed thermometer you will find it difficult to read the uth's temperature, dial thermometers won't do it, and guessing is risking your snakes health.
Generally the heat lamp will cover a portion of the warm end and a portion of the middle of the tank leaving the cool end cooler than the rest of the tank.