Tado V3: Thermostat precision, boiler relay cooperation and application problem

Hello everyone. I've been struggling for the last two days with a Tado room thermostat working in conjunction with a double boiler relay. Everything connected to the internet via a hub. Generally everything connected and cooperates with each other, but in my opinion the precision of the operation leaves much to be desired. (so it seems to me)
When in the heating scheme the set temperature is 19.5*C and in the room it is 19.2, the relay still does not start the boiler. It is the same with switching the boiler off. The set temperature is 20*C and the relay switches off the furnace at 19.6*C. Well I don't understand!!!
That's what this app is for! The relay has switched off the furnace, but the app still shows „heating is 20.0”
What are your experiences with this contraption? Maybe someone knows something that isn't in the interwebs…