RBI Sweaterbox Rack

Up until now - I have not needed the fourth/bottom tub in my RBI Sweaterbox rack but I've recently noticed that the top three tubs stay at the same temps but the bottom tub seems to run a bit cooler - why is that - what can I do to get them all at the same temps.

The rack has flexwatt backheat and it is regulated with a Helix Therm.

Help.

Thx

Normal... Heat is going up so lowest tub will be colder a nip...

What I did was to simply put a 1/2 inch thick piece of insulation between the bottom the rack and the floor. Worked great for me. Now all my racks are on wheels which keep them about 4 inches off the floor which also works.

My racks are on tables so would the insulation trick still work??