[ASA Coed] Blocking Safety Base?

[Stat-Man]

Had a scenario come up at a game last week played with ASA rules as the base set (plus local modificiations).

Batter hit the ball to the infield, and as the throw came to first, F3 sets up with the right foot on the white base and the left leg positioned to block off the orange base.

I realize that a fielder with the ball can block the base to his or her heart's content , but can a fielder do this?

It didn't matter in this play as the batter was not going to beat the throw, but I wonder what the call could be had the BR beat the throw and been hindered by this unorthodox positioning.

(Throw to F3 was not wild, errant, or coming from RF foul ground).