UTH necessary if ambient maintained?

So I have an UTH as well as a ceramic heater. I have one thermostat that the under tank heater was hooked up to for a while, but I had difficulty keeping ambient where it needed to be. I switched the thermostat and hooked it to the ceramic so that the cage temp would stay stable and repositioned the sensor to midway up the cage wall on hot side. I keep the setting at 87 degress which leaves the cage 82-85 degrees stable and constant.

My question is, do i need to also use the undertank heater? the substrate is just a degree or so off of what the thermostats read so, everything in the terrarium is a stable 84 degrees +/- 2 degrees.