The parachute affects drift less than you might think. The chute is small and is there for stabilization mainly (partially for arming), not for a soft landing, so it doesn't do much to slow the decent. I've seen BLU-97 drops during 15-20 mph winds - right at the limit of test parameters - and you couldn't tell the difference in impact patterns. Obviously there has to be some effect, but it's not that much.