First, Monobass, Your first photo showed you to be in the least practical and ergonomic wayof sitting/standing by being directly behind the bass (looking down the deck of an aircraft carrier !)
To flesh out your quote above I use the metaphor of the most natural way to clap your hands being together- in front of you and dead centre. The end of your fingerboard would be where your hands come together in front of you as you finish a three-octave scale with an up bow. The hands are doing different tasks as you play but work together best , individually and combined, with my imaginary arrow IMO. You can feel the difference in naturalness between glissing up the length of G string while using a long up bow or down the string with up bow. I should qualify this by saying that I use French bow, not German. The limiting factor when rotating the bass inwards is not to make a stripe of rosin on your leg. Rotating outwards throws weight back on your LH thumb and interferes with arm, wrist and hand movements. as well as making the G string harder to reach.
The other dimensional controls you have are the height of your stool and the length exposed of your end pin. Because there is no one body shape or height for each of us and we are all playing basses of different dimensions and shapes it is not easy to arrive at you best ergonomic and most comfortable relationship with your instrument. I found that I had to examine all the above again when I recently lost 10 pounds in weight. Good luck hunting !!