The foul doesn't occur during a loose ball play. it occurs during a running play. All of the action after the ball is caught is part of a running play. As such, the face mask foul is penalized from the basic spot, which is the end of the run. Tack it on.
Under the All But One, defensive fouls are also penalized from the basic spot, either the end of the run for running plays or the previous spot for loose ball plays.
BTW, welcome to the board!
