Okay. After doing some reading, I have found that (according to my research) the most likely explanation for what bbs do inside the barrel is:
A regular hop mound will apply a downward force as well as a backspin upon the bb, causing it to be forced to the bottom of the barrel and bounce along the barrel, until such a time as when the Magnus effect will take over from the reaction force of the top of the barrel, and allowing the bb to slide along the top. This would suggest, that when using a normal hop, a long barrel with a larger bore would be beneficial. Obviously, don't overvolume.
With an R-hop or some variant thereof, it would seem as though the bb is not forced down, rather the spin, because it is imparted over time, allows the magnus effect to hold the bb against the top of the barrel right away, which actually imparts more spin, if you think about it. This allows the bb to make small bounces along the top of the barrel, but never contact the bottom of the barrel unless a very tight bore is used. Later on, the bb will simply ride the top of the bore to the end of the barrel. This would suggest that a shorter barrel could be used, but again, that a normally-sized bore should be used - due to the fluid mechanics of the bb traveling down the barrel, a tighter bore will force the bb against the top of the barrel, stabilizing the spin much like an LRB.
R-hop and LRB will do much the same as above, but due to the bend in the barrel, the bb will stabilize against the top of the bore much more quickly, and will actually be able to gain some topspin from the top of the bore. This suggests a slightly longer barrel, again, should be used, and (I actually did the math here) that a bore diameter of 6.0347 is optimal to force the bb to the top of the bore and keep it there. This number will change as you change the μ of the bore (steel or brass) but it always ranges from 6.03321 (steel) to 6.0352 (brass). I put 6.0347 because it produced the most consistent output.