Go to http://www.dailymotion.com/video/x2nvhv_project-705-705k-alfa-class-russian_news
and watch the first part of the movie which shows the sail of ALFA Class Soviet SSNs in profile.

Note the sloping sides of the sail and how they are fared into the outer hull of the submarines.

The elimination of a sail with parallel sides (constant width) reduces snap roll, the tendency of
the sail to begin to act as a control surface during high speed course changes. This design
feature alone would have told the US the ALFA was a very high speed platform even had there
been no confirming acoustics.