I'm not sure what you mean. Do you mean the draw size of the camera widget in the viewport? Or do you mean the scene as it appears through the camera? If it's the latter there's no other way to control it besides lens fov mm (or render settings but they're directly proportional to the lens anyway). It won't affect the…
BSP is intended to be used for simple surfaces during certain parts of your production pipeline when you are blocking in a space with general shapes to get a quick feel for things. They are not intended to be the final solution. As far as for performance reasons, I'm not a graphics engineer, but I think it has something to…