When Watson and MM are in together, I'm pretty sure that Watson is still the 4 for all intents and purposes. He definitely is on offense. On defense, it probably depends a bit more on matchups, but I think Watson is still usually guarding the spot that King was.
However, MM has still gotten time at the 4 with 3 true guards. According to cbbanalytics.com, in conference play, the combo of Lipsey/Gilbert/Jones/MM has gotten 82 minutes, and combos with one of the three guards sitting in favor of Pav have gotten another 25+ minutes. A majority of those minutes have come in the last 5 games, so it seems pretty clear that as Jones has forced his way into more playing time, it's pushed MM down to the 4 more often.