As is often the case, I learned something new about mechanics from a coach.
Apparently the proper mechanic when you are responsible for a specific runner/base is to focus all your energy on said runner/base and not be aware of anything else in the game.
Sit:
I am U3, rotated (R1 only), base hit, R1 to third, BR in rundown between 1B and 2B (U1 has rotated home with R1's advance), R1 now tries for home and avoids tag with a nice sweep slide away from the catcher. U1 at home is straight-lined and can't see the missed tag, however I have the perfect angle at 2B and overturn call after a conference. Coach can't believe I could see the play because my responsibility was the runner standing on 2B.
Best part of the sit - when coach barked "Who changed that call", and I indicated it was me, he yells across the field, "Get over here" not once but twice; because of course I wasn't moving after he said it the first time, or anytime after that.