Need some help with Rack Temps

I am using a Reptile Basics VE 2 Shelf Rack. I have two VE thermostats on this rack. The main thermostat probe on the top shelf and backup thermostat probe on the bottom shelf.

The problem I have is that the probe slots on the rack are pre-drilled for probe placement and the drilled area does not go all the way to the point where the probe touches the flexwatt. There seems to be about 1/2" distance between the tip of the probe and where the heat tape begins.

I am having trouble getting correct temps in all tubs. I currently have 4 small tubs (2 per level) in this rack. It's either too hot or not warm enough. Very frustrating.

Does anyone have any thoughts as to what I am doing wrong?? I want to establish an 88-90 hot spot.

If anyone can help trouble shoot things with me.