If it's this one:
http://www.bintel.com.au/Astrophotog...oductview.aspx have you unscrewed the extension part so the EOS adapter screws straight to the glass piece in this photo:
http://agenaastro.com/catalog/produc...36/image/5604/
The agenaastro site does mention 70mm back focus.
http://agenaastro.com/gso-2-coma-corrector.html