haruspex said:
The distinction I am making is between physics, in the sense of physical processes, laws of physics, etc., and the art of applying a convenient subset so as to extract roughly correct results for real world problems. It is not the physics that is rife (not "ripe") with assumptions, but the application of our knowledge thereof.
Had the question specified a large group of riders and compared front, middle and back there would have been no issue. But with just three it would seem that the approximation you favour produces the wrong answer, so is by definition a too crude approximation to the actual physics.
Just one last thing. I want to tell you a story about a time my dad and I got into an argument (God rest his soul) during the summer between by freshman and sophomore year of college. That was the only summer I went back home, and he got sick shortly thereafter, so this was pretty much my last normal summer with him. And with me being in school to be a Chemical Engineer, and him a Civil Engineer, we had a mutual respect for one another's opinion.
He had purchased a deer slayer (or dear hunter, or something like that) .44 cal hunting rifle. It was basically a hunting rifle that shot .44 magnum pistol rounds. He was very proud of it and showing it off to me when he got it before we went to the shooting range to try it out. He shot it once or twice, and looked at me with a puzzled look and said "There's something wrong with this gun. I think the spring that absorbs the shock is set to tight." That didn't sound right to me, so I got behind it, took one shot, stood up, handed it back to him, and said "you're shooting the wrong, or bad ammunition". He immediately went into a tirade about how ridiculous that was, and that he had just bought it, and it couldn't be bad! We argued for about 5 minutes about this until I finally looked him in the eye and said, "Dad, if you could adjust a spring in a gun so you would feel more or less kick, why wouldn't marine snipers to that with their .50 cal sniper rifles that kick like a mule?" He looked at me with a dumbfounded look and stormed off muttering under his breath.
Two days later, he walked into my room with two boxes of ammunition. He held up a box of .44 cal cartridges (I almost called them bullets, but I figured you might call me out on that) and said "I accidentally bought these when...", he then held up his other hand with a box of .44 MAGNUM cartridges and stated, "I should have been using these". I was lying on my bed, my body facing away from him, but I was looking over my shoulder at him while he spoke, and when he was done I simply lifted my thumb up. He then said "I still think there's something wrong with that damn spring..." as he walked away. I just smiled and shook my head.
We had a similar argument when I tried to explain to him that table salt (NaCl) dissociates to Na+ and Cl- when dissolved in water. He died still believing that they floated around as little NaCl molecules in the water, so small you couldn't see them, but still together as a molecule. And he died around 8 years ago, so even the internet couldn't convince him despite overwhelming evidence (go figure).
So that's basically what I'm doing here. I'm shaking my head, smiling, and walking away. Bash me or the basic physics all you'd like. If anyone else has any questions for me, feel free to ask, but I'm not going to get into a "dad conversation" with you. For me at least, those conversations died with him.
I wish you luck on your quest to find the precise location that receives the most benefit for every possible eventuality. When you go crazy trying to do so and change your name to "Plays Worth Squirrels", grow a long beard you keep an open lollipop in, and start writing your life's memoirs (bonus points for those who catch the "Boy Meets World" episode - what can I say, I had a crush on Topanga), don't come crying to me... :)