Vuforia ground plane always scale model to 3/4 screen height

What I’m trying to do this have a 3d model project it onto a surface of a 3d object but Always have it scale to 3/4 of the height of the screen regardless of where it’s placed or the angle.

What I tired to do was use the height of the object and convert these points into screen space then divide the height by 3/4 of the screen space