I have two HomePod minis which are less than 4ft apart, at the same vertical and horizontal planes (either side of a TV).
The "thermometer" difference between then is generally 1.5-4.5 celsius 😂😂😂😂
They also differ substantially (about 4.5 celsius) to the temperature reading on my Tado room thermostat, but in fairness that is in another room and permits offsetting for "feel".
I might have to go and buy an old-fashioned mercury thermometer. 😂