I just bought my first tub rack.

It's a 5 slot, 32 qt PVC rack from Boa Master.

It uses 12 inch heat tape down the back.

I currently have the thermostat set to 100 degrees and I'm reading about 86 degrees inside the tub.

What is the "typical" thermostat setting to achieve a 90 degree hotspot on the floor of the tub?

And is this even possible using back heat?