First, please check that the installation of the Smart Valve is correct (see the installation instructions in this section) and that the hydraulic operation of the valve is optimal (e.g. internal drawing; for this and similar verification a technical intervention might be necessary).
The Smart Valve could be installed in an unfavorable position (e.g.: at the bottom of the radiator, too close to the floor, next to windows draughts).
In this case, you can set an "offset" (temperature difference of 0°-5° more) through the app, by selecting "Menu --> Devices --> Smart Valve": then, select the valve in the room by clicking on it and click on "Optimisations".