Whatever you're data is, it's pretty clear you've misinterpreted what it means.
Which says you neither read or understand that there is a scientific quantification to pressure differential from bleed down. Even in a highly dynamic situation such as a bullet going down a barrel.
Why do you think your question about the M4 vs A2 relates to the discussion? Obviously the shorter barrel is slower, duh. Your claim that the barrel length after the gas port doesn't accelerate the bullet is completely wrong, along with most of the other stuff you said too.
Like as said above, if you say you're right, go build a long barrel rifle rifle with a short gas path. A standard port is about .4 of the diameter of the barrel. That is a significant amount of gas, not a negligible amount. What YOU don't say is that with gas path length increase on same length barrels, velocity goes up. And, yes I have shortened barrels from 24" down to 18". The drop in velocity was under 10 fps. No, once the bullet passes the port there isn't any acceleration. At least not enough to brag about.
Have you ever shortened an AR barrel and compared velocity? If you had, you'd see lower velocity with the shorter barrel in most cases. That tells us the bullet is still accelerating in the last few inches past the gas port. There is plenty of data showing this online.
Again, it really doesn't matter at this point. He already has a barrel he can use. And, if you agree with Jake that a pressure port location doesn't matter, why aren't YOU using a carbine gas path for everything?