Hi,
Unfortunately, it's known issue, that 3ds Max is not always showing procedural maps correctly in the view-port. To match the
Noise map (any procedural map) used as the
Distribution map in the Forest object, it should be aligned to object (for use of the
Object XYZ) or to the world's coordinate center to match
World XYZ. Attaching screenshots.
Changing the
Size value should affect the distribution correspondingly. If it's not so, I would suggest you to adjust the
Distribution Map -
Threshold value (that defines the conversion to black/white levels).
Hope that helps.
Best regards,