Often in the winter when starting from cold a slightly richer mixture than normal will be ideal. Used to fly an aeroplane with a choke which on initial start would give a very rich mixture ideal for starting and the first couple of minutes of running. Once started gradually losing the choke kept the rpm at peak. After a short warming period it would be far too rich and start spluttering black smoke.
Anyway, I found through experimentation that the carb heat would often have a similar effect on startup; the freezing cold (and therefore lovely and ‘thick’) air going in to the freezing cold block liked to have a much richer mixture than could be set with full rich in the mixture control; therefore warming the air going in to the carbs using a little carburettor heat had the effect of lowering the air density and therefore creating a mixture much closer to optimum for running. All a bit counter-intuitive really when seen in action but totally normal.
In summary, the way I visualised it was: Very cold dense air in to a cold engine = mixture a little lean of peak. Slightly warming the incoming air before sending through the carburettor => richens mixture slightly taking it closer to peak. Once the engine warms up to operating temperature, mixture will be rich of peak and therefore getting rid of carb heat will make the engine respond in the way you would expect.
Interesting to play around with in any case - hope that helps!