The speed of pitching machines is measured exactly like it is from a real baseball pitcher - from the release point.
Radar guns measure a pitcher's speed from the point where the ball leaves the pitcher's hand. Radar guns measure a pitching machine from the point where a ball leaves the machine.
Therefore, it's 52 MPH at its release point no matter how far from the plate the machine is. It won't cross the plate at that speed whether it is thrown by a person or a machine. At 60' 6" a baseball loses 10% of its velocity by the time it crosses the plate.