Interesting idea re: carb icing as that is not something I've ever experienced (at least, I don't think so - I used to ride my original M900 year-round in NZ, and in Wellington the winter days do get down to low negatives on occasion). I think I've still got the heater tap off, so while the 'outlet' will be pumping oil in, it wont be going anywhere, so I'll try a ride with the heaters properly on and see what happens there.
Otherwise I had also come to the conclusion that I either need to adjust the mixture screws or adjust the needle clip (or both).
Funnily enough I had been reading around various places and managed to glean that this is probably a needle to main transition issue. I need to be a bit more attentive to ensure it is only in the 4-4.5k region, and not around 3.5k as well, which would apparently indicate problems in the pilot circuit also.
Obviously adjusting the pilot is a bit easier than moving the needle clip, but hey-ho
Btw the clip is currently sitting in fifth from the top.