I have only bottled two 5 gal batches thus far. 1st time was an amber and I forgot to cool the previously boiled water/corn sugar solution. The amber had it's own problems (too sweet, my fault) but it was evenly carbonated.
The second batch was a Sierra PA clone that was much more like what I was shooting for (yeah!) but I've found extreme fluxuations in the carbonation. Considering how I would box capped bottles as I completely them, it's safe to say that one 12-pack would be 12 bottles that were filled in order. I found I had one 12-pack that contained over carbonated bottles, compared to the other 12-packs. I believe it was the 1st set of bottles filled, so it consisted of the beer from the bottom of the bottling bucket. I poured into pint or even 22 oz glasses and watched them fill with foam (3/4 foam). The aroma was fantastic seeing that the overcabonation was driving the aromatics out.
For this batch I had boiled the corn sugar in water and then cooled in an ice bath. It may have even been cooled below the temp of the beer I was racking from the fermenter (which was around 66-67°). I started the siphon and poured in the priming solution slowly along the side of the bucket right away, so it was in there before 95% of the beer had been moved. I did not swirl or mix, I simply relied on the beer ciming in from the siphon to mix with the solution.
Would the temp of the priming solution being too cold cause it to sit at the bottom of the bottling bucket despite the beer being siphoned? If so, it would explain why the first bottles I filled were overly carbonated in the end. (all bottles were then stored together in the same closet, experiencing the same temps (mid-upper 60s) for carb'ing and conditioning.
I'm bringing this up now because I will soon have my bavarian hefe ready to bottle, and am considering not cooling the solution if it will mean a more even distribution of the priming sugar