A lot depends on chemistry of course, those outer rings need lube, grinding, tongues, and slow insistence and the tightest boys will let you on in. And start to feel that head against their insides and now the pleasure starts. Of course depending on anatomy, getting balls deep might require punching thru the deep ring (bend).
The deep ring is trickier to open sometimes - and where you have to feel the bottom out and decide how much resistance, how much he's grunting when you push into it - and how much more cock he's gotta take. Usually with a little time and pushing a bit more every few thrusts, it will let you in. Sometimes you need to try a different position to get things to bend around a bit differently to initially pop that deep ring open. Make the angle a bit easier.
But sometimes once its warmed up and its close but not quite open, a little muscle definitely does the trick 🙂
But its so worth it.