3 Man Tag Ups -ASA

[Chess Ref]

Gonna be doing alot of 3 umpire games this weekend. So it's a good chance for me to get a little better at this. I'm going over page 228 and some of the info has me a little puzzled. I'm hoping for some clarification here.

R1 at 1B. we have a fly ball that neither ump goes out on. The book says the tag up responsibility is the 1B ump.

So what happens to the 3B ump who started the play in the B slot. Does he just hang around 2B and watch the play ?

It seems to me that you're gonna have 2 umps standing at 2B on this. I'm assuming I'm missing something here.

Feedback please....