Maybe the ceiling panels are heating the thermostat hotter/quicker than the air since they are radiant (radiant needs a mass to heat, won't heat the air directly). Also, you need a known good thermometer or temp probe for your meter to see what the room temp really is, then you can go off that. I don't think the cheap little thermometer built into the front of the t-stat cover is a highly accurate instrument. Start with your accurate thermometer, and then see how far off you are. Leave the t-stat alone for at least 6 hours to let the room temp stabilize.
