Looks like you have a good list to start off with.
Position sensitivity is a hard one to predict. Deterrent coatings or no coatings. Size and shape of kernels. How they pack. Not only does these differences effect burn rate but how the pile is affected in space at time of ignition. Chemical makeup can be chosen. Some powder ignites easier than others. But I think this is a minor thing here. If it was major, all bullseye shooters would be using the same powder. My guess is that the momentum of that big long bullet will smooth out some of these reactions going on behind it.
The base of that bullet is going to be on fire anyway from those Win SP primers. Ha!
