Here is a response from David Laville, a GSEM, earlier this year, from a thread on R.S.G.
"Some people say the sensation is like you're unwinding your shoulders while keeping your back to the target"
"I'm going to explain this with two scenerios.
The first is swinging something heavy like a Momentus, a broom may
even work. Swing the club, or broom, to the top. Let your arms and
club fall. They will fall while your right shoulder stays back, it
will not move out and forward. The right shoulders staying back and
turning down is what some people say is the sensation like you're
unwinding your shoulders while keeping your back to the target.
The second is to hold a club across your shoulders. Lay the head end
across your left shoulder and the grip end across your right. Turn
your shoulders so the grip end of the club points at the target line.
Note that your right shoulder works down and not around flatly. This
right shoulder motion is what start"s the club down on plane."
On the Chuck Evans(GSED) forum, Chuck has an article addressing OTT. Essentially, one keeps the right shoulder back while initiating the hip slide to allow the amrs to drop.