Different encounter types have different distributions, which sometimes affect the number of IVs locked to max. Here's a chart I made to analyze the odds for the various possibilities; more recently than this chart was made, the various star levels of Max Raids have come into being as another source of IV guarantees (albeit Max Raids only exist in games where Hidden Power is not a selectable move, but those games still know how to compute its type, and that type does at least have minor relevance in its interaction with an opponent's Anticipation ability).
The columns you'll probably be encountering most frequently are the 0 (most random, unmanipulated encounters) and the 3 (all legendaries in XY and beyond, and a few other niche types of encounter). With no IV locks, Bug/Fighting/Grass are all tied for most common, while the 3-IV lock makes Dragon the most common type by a wide margin.
