In Semi-Closed or Promenade position, your lead shoulders are turned a little bit outward. The man turns his upper body a little to the left, and the woman turns a little to the right. Both might be looking down line of dance.
In Reverse Semi-Closed or Counter Promenade position, it is the trail shoulders that turn just a little outward. It is the man who turns a little to the right and the woman to the left. Notice that the arm positions do not in any way "reverse," only upper body relations. Both might be looking toward reverse line of dance.
There are small changes in hand and arm positions. The man's right hand must move more to her shoulder or even upper arm, as his right side moves away from her left. His left hand is held a little higher, and the lead shoulders will be retracted or held a little farther back than in Semi-Closed.
Reverse Semi-Closed is a diffucult position in the same way that Sidecar is difficult. Ideally, the lower body should still be positioned a bit to the left (in Semi-Closed position; in Sidecar, the lower body should be in Closed position). At the same time, the upper body is shifted a bit to the right. Do we feel a little like contortionists?
The b&w composite photo shows Victor Silvester and partner in semi-closed position on the left and in reverse semi-closed on the right. Click for an enlargement and to compare the two dance positions.
Brent and Judy Moore's foxtrot, Breathless, makes nice use of Reverse Semi-Closed (and uses the ballroom term). In part B, we do a Hover Telemark to face line and center; a Feather still facing line and center; and then Counter Promenade to Extended Fallaway to a Back Wing;;; (that's a "slow," eight "quicks," and a final "slow").
The key step is the first one. We are in banjo position. The man steps forward left and the woman back right, both turning to the left to end in Reverse Semi. The next two steps are forward right and forward or thru left for the man (forward left and thru right for the woman). This sequence illustrates the nature of Reverse Semi well. There is a tendency for the woman to cross behind, but don't do it. Just as you would step together, forward on the lead foot and then thru on the trail foot in Semi-Closed, so you step forward on the trail and then thru on the lead in Reverse Semi.