AFAI have seen the "problems" with stadimeter is not the stadimeters fault, but rather inaccurate masthead-heights, and as in the above case, inaccuracies in the map.
You can double check stadimeter readings by using Arclights new periscope mod (which is extremely cool AND presents the most realistic graticule image i have ever seen in the SH- series at all)
http://www.subsim.com/radioroom/show...=165408&page=2
Awesome mod - a must use mod in my humble opinion.