I really am not a fan of the thought, “hit down on the ball.” The golf ball is struck three different ways depending on the club and ball position. Woods off a tee are hit with an ascending blow and are played near the lead leg heel. Woods and hybrids off the ground are hit with a sweeping motion, ball 1” back of lead heel. Irons with a descending blow, 2” back of same heel.
The key to hitting irons correctly is for the hands/grip to be in front of the club head, creating shaft lean and moving the bottom of the swing arc in FRONT of the ball. This creates a descending blow and a small shallow divot in front of the ball.
The problem most folks have is they try to help the ball up in the air. They do this by swinging the club head rather than the grip. This causes the club to bottom out behind the ball, the result is fat and thin shots.
Here’s a great drill to feel a descending strike. Draw a line in the turf about 2 feet long perpendicular to the target line, grab a wedge, NO BALL, set up with about 65% of the weight on the lead leg and leave it there. Take a slower pace take a half backswing, on the forward swing focus on swinging the hands/grip back down, club head lagging and try to brush the grass in front of the line. Keep doing this until you can do it every time. Then put a ball on a tee on the line and again, focus on brushing the grass in front of the line.