[brandda]

Big field or little field? From the way you are describing the jam up, it sounds like someone was using big field mechanics on the small field.

On the small field, the FU lines up usually on the outside of the base paths to prevent exactly what you are describing. On the big field, however, B and C are both in the same place on opposite sides of the mound. Split the difference between the mound and second for distance and then line up in a straight line between the left or right edge of the mound and home plate (think of a V).

As to the obstruction issue, unfortunately the umpires are part of the field and it is the responsibility of the players to work around them. I personally try to shift a little one way or the other depending on how I see the fielders positioned, but you cannot move too far or else you risk being out of position for a call.