Add a note about thermostat behaviour differences between heaters.

README.md

@@ -158,6 +158,8 @@ When switching to Anti-freeze mode, the heater will set the current power level
 
 When child lock is enabled, the heater's display will flash with the child lock symbol (`[]`) whenever you change something in HA. This can be confusing because it's the same behaviour as when you try to change something via the heater's own control panel and the change is rejected due to being locked, however rest assured that the changes _are_ taking effect.
 
+When setting the target temperature, different heaters have different behaviour, which you may need to compensate for.  From observation, GPPH heaters allow the temperature to reach 3 degrees higher than the set temperature before turning off, and 1 degree lower before turning on again.  Kogan Heaters on the other hand turn off when the temperature reaches 1 degree over the target, and turn on again 3 degrees below the target.  To make these heaters act the same, you need to set the Kogan thermostat 2 degrees higher than the GPPH thermostat.
+
 ## Fan gotchas
 
 In my experience, fans can be a bit flaky. If they become unresponsive, give them about 60 seconds to wake up again.