A characteristic of the exercise is that uke feels like he's pushing into an unyielding object throughout the entire exercise even though nage's shoulder is retreating during the initial phase of the movement.
We have a lot of paired exercises where nage moves while being pressured by uke via pushing or pulling.
At issue is how you receive/absorb/disperse/redirect/etc the incoming attack and energy. In this case the shoulder is the point of contact. Iif you hold it at the shoulders then you have disconnected from the rest of the body. The shoulder can be firm with everything passing through as long as everything is connected. By the way.......the shoulder follows it does not initiate, same with hips....they follow. If you initiate with the shoulders you have disconnected. How I see it......... And I think this is the road Gerado is traveling..........