I just re-read your original post and, if I'm not mistaken, only one side of the flange needs to be isolated. Depending on which side the isolator/insulator unit is positioned (and if they can be positioned either way). Obviously, if your Capac readings improved, the extra washers are needed so good deal. My experience with a shaft being grounded to the hull, the Capac readings suffered more severely than .1 volt, which may be an indication that something else might be improperly grounded... but again your readings improved so my analysis is probably flawed. Anyway, just thoughts.
Jim
Jim Hemphill
Detour
'87 32' FBS, USCG Certification #1057921
Berthed MM 207 Tennessee River, Picwick State Park Marina