Cold crashing, priming and carbonation

I have a conundrum on which temperature to use when estimating priming sugar, my recent experience contradicts everything I have read.

I have always calculated the sugar based on the current temp at bottling, which has usually been around 10c. But lately I have been cold crashing my beers to below zero for extended periods (mostly because I am too lazy, or busy, to bottle right away), the last one was over 2 months.

About 4 brews ago when I worked out the bulk priming (in beersmith), my beer was around -2, (which I rounded up to 0 to account for time to siphon etc). The result was, for my mildly carbonated preference of 1.6-1.8, that it only needed about 8g dextrose for a 23L brew. Seemed odd but I went with it anyway and within a week at room temp the beer was perfectly carbonated.

Everything I have read seems to indicate that this should not work, but for 4 consecutive brews it has, mildly carbonated with a frothy, persistent head, just how I like it. I am confident that the beer has finished before crashing and fairly sure I can rule out infection (the last bottle of my most recent brew was 6 months old and no sign of infection/over carbonation).

Just wondering if anyone has any thoughts on this? It just seems too easy, I bottle straight from the fridge, give it barely any time to warm up, and the big benefit (other than crystal clear beer) seems to be that they are carbonated quickly, no waiting around for the yeast to wake up, or worrying if it will.

Cheers,