F6 covers 3B, F4 covers 1B, and I consider the coach who bunted a complete idiot unless it is for the purposes of a squeeze. Why would you give up an out to move a runner up to 2B.
I've seen teams bunt in this sitch with great effect, I guess a variation of a safety squeeze. Bunt targeted towards F5....if F5 crashes to field it, then the runner on 3B can come up the line a good ways (no one immediately covering 3B) and see what F5 does. On any play to another base the runner should score easily - basically no different than a sac fly result. If F5 holds the ball, all runners safe. If F5 hesitates to crash and F1 comes over to field, she has a tough throw to either 1B or 2B and again, the runner on 3rd has a good chance to score. Or she forces the runner back to 3B and everyone is safe. If F2 fields (then the bunt wasn't placed well) she can check the runner at 3B and throw for the out. The chance to score from 3B probably depends on the runner and the level of play in this sitch.
