[AtlUmpSteve]

I believe it is best to learn the general rules than specific cases. Assuming BU doesn't go out on the fly ball (and it doesn't matter what field the ball is hit to):

PU always has 3rd base, BU always has 1st base. If single runner at 2nd, BU.
If multiple runners, PU always has the lead runner, BU has all trail runners.

Those are the standard rules. If BU realizes a ball hit to right and down the line will present a challenge to PU, then BU can communicate "I have your tag at 3rd". Otherwise, if no communication, the standards apply.

Some may get on here telling you to pregame this; it is poor advice to pregame a variation. Only let a play determine if a variation is necessary, don't preplan to vary.