I'd like to see someone do properly rigorous statistical work on this, but my current leaning is that the more granular you get with SV%, the more you're going to struggle to pull trends and find predictive value in it. Only 5 goalies in the league saw 400 or more HD shots against last season....that's not a lot of events and there's a pretty big variance in the quality of chances even within HD. A breakaway is a HD shot, and has a league wide shooting percentage of ~30%. A 2 on 1 shot would also be a HD chance and those have a shooting % of closer to 50%. Rebounds have high shooting %'s, etc. The fewer the amount of events that are considered to "matter", the more that things like shooter quality and team quality will create noise in the results and make the statistic useless for future prediction.