It's not carbonated. Let's say I'm targeting 2.5 vol for 20L of beer. If the beer is at 40 *F there should 1.5 volumes of residual CO2 left in suspension from fermentation. So I need to add enough sugar to generate 1 vol of carbonation, which would be 83.6g of dextrose.
If that same beer were 80* F, there would be 0.7 volumes of residual carbonation, so I'd need to add enough sugar for 1.8 volumes of carbonation, which would be 142g of dextrose. So at 40 *F there is twice as much residual CO2 as there would be if the beer were 80 *F at bottling, and it requires half as much priming sugar, according to the calculator.
When I transfer from the carboy into the bottling bucket, I must lose "some" amount of CO2, and I must lose "some" amount of CO2 when it foams up in the bottles, and I must lose "some" amount of CO2 as the cold beer in the bottling bucket warms up and off-gasses. I don't know how much the "some" that I'm losing is, or if it's enough to significantly change the amount of priming sugar I need to add to get my desired carbonation level.
If I lost half of the residual CO2 during racking/bottling, at 80 *F that would be 0.35 vol and at 40 *F that would mean 0.7 vol. If I'm targeting 2.5 volumes, that could seriously throw off the carb level. If I only lose a quarter, that wouldn't be as bad, but it would still fall pretty short of my target. But maybe I only lose 1/20th of the carb level and it's not an issue at all. That's what I'm trying to figure out.