After further consideration prompted by this thread, I have taken the seven quarter stack out of the AR9 buffer tube. With the quarters at the back of the buffer tube, the bolt travel is limited, but the recoil spring is given a greater than standard pre-tension. Further, impact of the bolt, even with its buffer, tends to cause some rebound off the quarters. I have put in a plastic spacer that fits snugly inside the recoil spring at the back of the spring. The spacer is approximately the same length as the height of the stack of quarters, and should cause less bolt rebound.
I have not yet fired the carbine, but the rear impact of the bolt feels more damped when manipulated by hand. And, as expected, since the length of the bolt travel is limited the same amount as before, the LRBHO works.
MHO, YMMV, etc.