The video about sound reflection in rooms.
The tweeter is very directional and easily controlled. On the other hand...think about the bass signal being sent out of the subwoofer directly and then reflected off the back wall. At the same time a bass wave is sent out of the main speaker AND another wave is sent out the port or ports of both the main and the sub.. All bass sources arrive at different times. What a mess. Muddy bass is the result and moving speakers around won't fix this problem.
THIS is the most difficult to understand and control and the biggest singular thing that makes music sound clear, dynamic and impactful. If you don't have the bass right you've got nothing. Everthing else is secondary.