I usually stick my humidty gauges in the middle of the tank on the wall of the tank (not too close to the top of the tank). I don't think it matters too much so long as it's not near the top, or laying against substrate or a water bowl.
As for the temperature, I'd recommend getting a digital thermometer with a probe if you can for the warm side and stick it under the substrate under the hide over the heat pad (as this is where the snake will most likely go). You can't really do this with the thermometer you have now since it was mainly designed to get the air temperature. Your snake will spend mos tof it's time on the floor of the cage, or under the substrate, hence why the probe is better.
You can still use the sticky thermometer to measure the cool side or the general air temp if you want though (if doing this, i'd recommend resting it or housing it close to the substrate on the cool side), but probes are always more accurate and better. Just get a probe thermometer at least for the warm side and it'll save you a lot of problems and guesswork later.