Thank you both,
I’ve done some more testing and it turns out that the lens length and perspective angle don’t really matter. It works at any angle or length it seems. The only difference is how much of the object that you see. The wider the angle (or shorter the lens length) the smaller the object appears in the view port.
This seems to be a feature of two point perspective in Rhino. Not sure how it works that way, but I’m happy that it does.
Once I do some more testing to make it full proof, I’ll be telling my students to set their viewing angle to 45 degrees. (they can then scale the drawing as needed).
Andrew