You are using a RHP for the hot spot?
nice to know it is far far better than the old units +/-2ºF and 5%RH is reasonable. (twice as accurate across the board)
Is your ambient air temp taken from a place out from under the RHP and away from the any other heaters? Is the ambient air possible effected by the RHP? (in line of sight?)
That is a crazy high amount of humidity! 21gm/m3 (I used 78/88)
What is the room temp?