OK, this is my take on it. Forget about focal lenght! First decide your point of view, where is the person observing the scene standing? Got it, OK put the camera there. Now adjust the focal length to include as much or as little of the scene as you desire. Focal length does not change perspective, the point of view determines perspective, and from any particular POV the perspective will always be the same no matter what the focal lenght. What focal lenght determins is the width of view, hold a bit of paper with a suqare hole in it in front of your eyes, move it further away, you will see less of the scene, this is the same as chainging the focal length to a longer length. Your document window is the hole in the paper.