That does seem normal. But if 1 tub is getting 95f over the hole tub that's on the flexwatt and the tub underneath is only getting 95f at 1 or 2 points and the rest is 80 then that could be the temp difference.
Reading that back doesn't make as much sense as it did when I was writing it lol. Do you get what I mean ?
Maybe leave the tub on there for a bit and then take the temp of different parts of the underneath of the tub to see if the tubs are getting consistent heat