Mark, this is the age old problem of the early sensor position n the back of the RH head.
The issue is that the sensor is a type really designed to go into a waterjacket or radiator. On the air cooled Guzzi engine it screws into a poxy plastic fitting on the back of the RH head. The thing is the tip of the sensor rarely touches, or even comes close to, the material of the head itself. This means there is an air gap and as you know air is a great insulator! This means that on most machines that use this system the temperature detected by the sensor will be far too low. Throw in cold weather and it becomes even worse. It's this single fact that accounts for most 15M/RC and 2VPC W5AM having such wildly different fuel consumption figures in summer and winter.
The solution is to ensure an accurate, or at least more accurate, temperature reading and this can be achieved by adding some form of 'Thermal Paste' in the holder that the sensor screws in to. I use zinc based anti seize! It works a treat! When this is in there it means that rather than sitting in an air pocket the sensor sits in a sort of 'Deep fat fryer' and temp transfer is much improved allowing the ECU to work to more accurately govern the fueling.
*WARNING* The stock plastic holder for the temperature sender is very fragile. After the thermal paste has been added the sensor should only be screwed back in loosely and then the motor started and allowed to get good and hot! As it warms any excess paste will expand and, as long as the sensor is still loose, ooze out of the holder up the threads. If it can't do this thermal expansion will crack the holder and you're back to square one. Once stinking hot loosen the sensor right off before slowly tightening it down, (Be prepared to burn your fingers if you aren't careful!) you should then be good to go. Check your temp reading with Guzzidiag and be amazed at the difference!
For the very best solution replace the temp sensor holder with one of the brass ones used on the early Hi-Cams and 1100 Sport-I's. That way you don't have to worry about the cracking of the crappy plastic holder. These though are, I believe, made of rocking horse shit.