Sean keeps moving away, quickly reloading the rifle, then turns back at the monsters. The plan was well and good, but he had some new information to check. "Just testing a little hypothesis..." he says and shoots a long burst at the nearest lot.
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Round 1: 2 yards => 5 yards (3 steps back, end up facing the monsters) => monsters move 4
Round 2: 1 yards => 6 yards (turn 2, move 5, end up facing away) => monsters move 4
Round 3: 2 yards => 7 yards (move 5, turn 2, end up almost facing the monsters) => ...
Extra effort to reload and extra effort to move and attack, ending up with 5/12 FP.
If this has the desired effect and the men on the roof get it, they might want to aim at those brains-like things.
UPD: What about the grenade?