As a Magnolia grower- within each lot of trees-all planted in same medium (soil),
nutrients and watering evenly.
I think it comes down to the Japanese Maples, Magnolias, Dogwoods or other individual DNA(s)-some of the same lot grow slower to the Magnolias max, some in same lot grow very fast to trees max...
When I get questions on a certain variety I go out and look at those lots, and choose the best or two (flag, to identify) when I video.
Andrew