If you are outside the marker (outer marker), at 250 knots, clean. You then draw a dot on the windsheild to correspond with your runway landing spot. Then you change airspeed and slow for landing (forget about flaps and gear). The pitch angle gets higher as you slow, so you drop the nose to keep it on the spot, you sink and hit the ground prior to hitting your spot.
If you are at 250 knots and draw the dot. Accelerate to 400 knots in the dive. Your AOA will decrease so you will need to pitch up in order to keep the dot on target. You will overshoot. You will have to keep the dot off target at a higher airpeed than you first drew the dot in order to hit your target. Plain and simple.
You draw your target at 7000 feet. As you decend the wind changes 30 degrees to the left (or right, depending on hemisphere). You keep your dot on target and "home". You are traveling 8 miles per minute over 5 miles. You'll be lucky if you can home it.
You cannot hit any target unless you maintain a constant airspeed and altitude.Thats why HUD's hae a "Flight Path Indicator" that change with airspeed and configuration.