From what I've heard - Females generally stay towards the cooler side while building, and then hug the heat after ovulation. If she's still eating and digesting, though, that may be why she's on the heat, and 85 hot spot isn't very hot. Last year my females were hounds up until about 4 months before they laid. For 4 months prior to laying they had no interest in eating, but some eat all the way up until laying. One of my girls last year ate a mouse two days before she laid.
I second the idea of palpating with a t-shirt or cloth so that she slips through your hands easily.