Hi, when we installed the Tado system in our house we came across the same discrepancies between what the Tado radiator thermostats said and the actual room temperature was. A product of having the sensor next to a hot radiator I suppose. We searched this forum and discovered that like you we were not alone. You can set the offset for a Tado valve to try and resolve this, and this may work for you, but we found that the variation between room temperature and the Tado radiator thermostat (SRT) changes. So manually setting the offset and forgetting about it was not a viable solution.
To get around the problem we have created a wireless temperature sensor that integrates into your Tado home system, with an accompanying app to set it up. The sensor measures the actual temperature in the room several times an hour and automatically adjusts the SRT valve(s) in the room.
This is working really well for us correcting the system to keep rooms at the correct scheduled temperatures. We, like other people on this forum, love our Tado system but weren't willing to spend an additional £90 per room for a temperature sensor. Our wireless temperature sensor will cost about £20 and should be available in about 1 to 2 months. If you are interested then message me and I will let you know when they are ready.