IMHO your theory is wrong. The reason the 16" has more recoil than the 10" is because the bullet leaves the barrel faster (because more powder gets burned). Basic conservation of momentum... "for each action there is an equal and opposite reaction".
For a given barrel length and ammo combination, felt recoil can be mitigated by increasing the weight of the rifle, decreasing the reciprocating mass, adjusting the rifle's gas system to change the nature of the gas impulse (e.g. go to a longer gas system, adjustable gas block etc.), and adding a muzzle brake. The oft-cited solution of a heavier bolt carrier has the effect of softening perceived recoil because the impulse is less sharp - more of a shove than a punch. However, to shorten recovery time, you actually want to go to a lighter carrier so as to minimize the reciprocating mass that hits the back of the buffer tube. A lighter carrier should be coupled with an adjustable gas block so you can trim the gas to the minimum. Of course, this also has the potential to make the rifle less reliable, so think carefully.
I see, that makes sense also.