It's definitely been an interesting winter for the polar vortex (and so different from last winter)! When the polar vortex winds are strong, on average, it's sitting more over the pole and is more "round". But if you look at individual events/seasons, there's plenty of variety. That said, this winter has been interesting because it's been stretched a lot. Some of this could be due to the troposphere. If the tropospheric jet stream is stretched or extending down over North America, for example, then it could pull the polar vortex along with it. I don't know for sure that is the case this winter, but I'm sure it will be well-studied!