Gonna have to disagree with that part. In my experience there's only 2 things that matter here:
1) The size and wattage of the flex watt.
2) How many watts the Tstat can support.
I have 3 racks hooked to one Tstat. All 3 are using 3 in flex watt at 10W per ft. 2 are identical AP racks. The other is a RB type rack. All are holding the same temps throughout. The total wattage for all 3 is around 350 watts which is well within the Tstat wattage limit.
So where do you have your probe? If that would work it would be awesome!!
1.1 Normal
1.2 Pastel
1.0 Spider
1.0 Pinstripe
1.0 Mojave
1.1. Het Albino