I haven't noticed that being a problem, to be honest. Unless the radiator is situated so poorly that its convective current doesn't reach the whole room -- in which case, it scarcely matters how hot it gets -- the air temperature at the bottom of the radiator will be the heat in the room. Or at least, will be monotonic with the heat in the room, which is all you actually need it to be (that Honeywell thing is a neat idea if you don't like bending down to fiddle with the thermostat, but notice that it's calibrated 1-5, not in celsius or fahrenheit).

Peter