Do get too worried about the thermometer readings...they are good for reference but going by the chicks behaviors is better.
ETA: Oh, substitute 'MHP' for 'lamp' in my blurb below.
The best indicator of heat levels is to watch their behavior:
If they are huddled/piled up right under the lamp and cheeping very loudly, they are too cold.
If they are spread out on the absolute edges of the brooder as far from the lamp as possible, panting and/or cheeping very loudly, they are too hot.
If they sleep around the edge of the lamp calmly just next to each other and spend time running all around the brooder they are juuuust right!
I would think that the proper temperature setting of the MHP pad, seeing as it is supposed to be a surrogate for an actual mother hen, would be the normal body temperature of a broody hen.