Y'all don't know what "deep" is until you work men's A or B slowpitch.
Try F4 & F6 about 20'-30' beyond the baseline with F3 about 15'-25' behind 1B. And then F7 inserts himself about 20' behind 2B.
(and remember, there is stealing there, too).
I agree with Steve. This method is basically to satisfy the rules as they pertain to an umpire being hit by a batted ball which has yet to pass an infielder other than the pitcher.
It is a good mechanic. Recently, I've seen umpires come back from a NUS and using this mechanic, end up literally standing forward of a fielder. I'm not talking about a couple steps in front 15'-20' to the side, but about 4 steps in front less than 10' away.
While standing behind an imaginary line satisfies the rules, an umpire still needs to make sure they are in a position avoid getting involed in a possible play. Avoiding interference doesn't mean crap if you have a player run over you or take a shot by a batted ball.
And, like others have mentioned, I, too, will give a call @ 2B a higher priority in positioning than 1B for the same reasons.