I think I figured out why I was so confused. I have all soft torso bodies..LOL! Not just soft bust. I didn't realize they have regular hard bodies, soft bust, and soft torso(so the entire torso is soft including the bust). The bodies I have have a peg that is more cylindrical shaped that goes inside the head.
I ended up using the second size cylinder rather than the first. The first was a little loose, but the second seems nice and tight, I just hope its not too tight and wont damage the head..:/ It was a little difficult to get the head on over it, but I was able to do it.