Turning the heating water temperature down may help. You only get the stated efficiency when the water return temperature for re heating gets down to certain values. On your boiler that appears to be 60C. They spec 80/60 which I believe means flow 80C return 60C, However they also spec 50/30 and 40/30 where due to the way they measure it efficiency is over 100%.
A bit anyway.
The catch. Actual heat output from the radiator depends on both flow temperature and radiator size. Lower temperatures needs a larger radiator for the same heat output. When the system is designed they assume a temperature drop across a radiator and should set it via the lock shield valve. It's done by attaching clip on thermocouples to the flow and return pipes on the radiators.
The gas board set my Dad's up this way eons ago. I'd hope all installers can do that now. They also curved a radiator to nicely fit under a bay window. Maybe some can still do that but times change.
The catch can be how your system was designed in the first place. 80C flow and a higher than needed return temperature may have been used. Afraid I can't remember typical numbers. 80C flow is likely to have been used as it results in a smaller radiator. Some systems early on were mostly aimed at background heating but will often cope with full or nearly so.
Thermostatic radiator valves will help anyway but may mess up condensing when lots shut off. Not sure about that, Depends what the boiler does. I'd assume it modulates power output and cycles if that is not enough. They get around the problem of having to accurately size radiators etc for the heat losses from the room. Bound to save gas.
