They enjoy the play. They do not do anything in particular.
Several factors contribute to this phenomenon.
Bottom dude has been primed, and rides on the same wave with his top. Async sex won't get you there.
Bottom dude feels like shooting. He did not JO 15 min before having sex.
The top has the right size, and knows how to hit the right button
Both dudes are taking their time.
The most exciting part is that bottom dudes loses control over his shooting. The top usually fucks his bottom's spunk out of him.
If the top almost pulls out after the bottom squirted for the first time, the bottom dude starts begging the top to ride in again. The only way he can come is to let the top literally fuck it out of him.