Flange leakage check_CII database

Hi,
I am performing flange leakage study using CAESARII Peq method.
And my doubt is regarding the value of gasket diameter in CAESAR database.

For a 10",1500# flange; CAESAR suggests a gasket diameter of 289 mm.

Whereas, If I refer ASME B16.20, the dimensional standard for the gasket being used. For 10", 1500# and R54 gasket, Gasket diameter is 323.85 mm. And b0 is less than 1/4.

Can anybody letme know, Why is there A difference in diameters?

Can anybody please provide more insight on this?

My cleints calculation sheet doesnot match with the report extracted from CAESAR II. Hence I have got a comment on the report.

The gasket diameter data is stored in the ".G" file in the SYSTEM folder. (Likewise the flange rating data is carried in the ".FLG" file in the same folder.) That ".G" file (e.g. ASME-2009.G) begins with this statement:
"Values are the average of the Spiral Gasket ID and the Wound Gasket OD".
You could say there is a trade off between convenience and accuracy.
Use better data if you have it.

OK. Thanks a lot Mr.Dave.