I would use the eleven inch heat tape and place it on the back so that it goes from the top but not all the way down to the bottom, so that it will only cover a portion of the back of the lower tubs. Place the thermo probe in the middle tubs. Less heat will reach the bottom tubs, and more heat will rise and build up for the top tubs. It will take some fudging around with the thermostat to get it just right but it should make that few degree difference.
But really, all of the frogs will do just fine if you set the warmer area to be around 80-82 generally.