[AtlUmpSteve]

I believe the issue is where and how the tag is expected to be applied.

From the defined mechanic, it would seem the expected tag is perpendicular to the base line; the BR to head more to foul territory, and the F3 reaching from fair to foul. By getting closer to the line, BU has closer to a 90 on that play. (That is also the angle where you would get the most help from PU.) Moving into the infield may straight line you on that tag, with F3 between you and the tag.

However, many swipe tags bring F3 up the line toward home, and then the swipe may be behind them, with the runner having passed F3. In that case, moving toward the line makes the tag a straight line, and also removes the angle (closing toward 0/180 degrees) determining if the tag happened before the BR touched the base. In those plays, moving toward the infield provides the 90 to the tag, and maintains an angle on the base. And, that play has very little chance of help from PU, who is now straight lined.

I was taught to read and react, that neither solution was 100%. Again, your primary reaction picks up the play without help, while the primary ASA mechanic focuses on the play where you would likely get help.