Hi,
Well it depends on the type of rack (open or closed ) I think - on mine the probe is taped to the heat tape behind the tub rather than between them.
My thermostat is set to approx (crummy dial type) 90f which gives an open hot end of 87.6f and 91.9f inside the hides.
Now with a decent digital you will actually probably see you have to set it above the temp to hold it steady - the fact I only have a dial means it is not accurate enough to know what it actually thinks it is set to.
Some people do not use hides in a rack system but my tubs are a little on the big side and the snakes use them if provided so I have just decided to leave them in there. They hold heat in a little so I had to re-adjust everything to take that into account when I put them in.
Remember to give everything at least 30 minutes to an hour to stabilise when you make any changes though.
And I really can't stress how much easier this is with a temp gun - wish I had bought one years ago.
dr del