Only the original 20” barrel rifles were designed to have 10k psi port pressure.Gas port position was designed around Mil ammo for a 10k psi at the port. Same with buffer/spring and BCG. Civies changed a bunch of stuff to 'tune' the gun - but it doesn't really need much.
With the M4 redesign they were forced into a carbine length system due to M203 grenade launcher cut on the barrel. Subsequently, it has a 17K psi port pressure.
I believe it was Armalite who pioneered the mid length system in the late 90s.