The idea here is that the party exists physically in the safe cell then leans into another free cell to attack from cover. In a 2x2 party formation the 2 on the right column would be exposed during the move.
Per the rules:
Half-steps or dividing a logical grid square into smaller squares is NOT accepted.
Kind of a gray area for me here -- could argue that it's straddling the party over two cells and is ok, or you could argue that's a half-step and is not.
Ok or not? Cheers!