Sorry, rule of thumb is an English phrase that means "in general." Basically when you aren't sure about something, falling back to the "rule of thumb" is generally a good idea. I hope I have explained the phrase accurately.
Yes, scale the room up, and then you can change the camera to fit the change in scale. You could use two cameras maybe. I would just script the camera to zoom in. camera_set_view_size(camera_id, width, height) is a function you can use for that.