drawing - How does the distance between stationary point and picture plane effect perspective?

I want to understand what happens when you increase or decrease the distance between the stationary point and the picture plane?

I tried drawing a border (approximately 9” x 12”) on a real window with duct tape to create a picture plane (using the area within as a transparent canvas).

My goal was to see what happens when I (stationary point) moved far away. The tree that fit nicely when I was at arms length suddenly got huge when I took a few steps back and eventually only the trunk was visible in the picture plane that I made.

My question is why did this happen and how can I relate it to drawing perspective?