A "chip region temperature" value needs to be provided when using the Owlstone stand-alone UltraFAIMS control software. The system uses this value to estimate how many volts to apply across the chip in order to produce the DF values you specify. The attached slide shows an approximation that can be used to calculate the temperature in the chip region for a given MS capillary temperature.
Note: it takes about 30 mins for the chip interface to reach steady-state temperature when heating up from cold. Peak positions will not be stable until temperatures have stabilized.