Mushrooms form where water is leaving the casing surface, so moving air matters as much as the thermometer.
DMR measures 31 g of water leaving one square metre of bed every hour at 17 C and 85 per cent humidity, and puts the permissible air speed over the bed at 15 cm per second. A dead corner with no air movement will not pin, even though the wall thermometer looks right. Air that is too fast and too dry crusts the casing and kills young pins.