Hi,
The conversion from Use Case Points in Function Points is a very delicate process.
It depends how the use cases have been written. There can be a use case that contains more elementary processes and another one that constituites a single elementary process.
To find a rate of conversion we have to establish some restricted rules to build the Use Cases.
In any case the question is : if we want the function point why don't we count them?
A good counter can have a productivity of 100 FP an hour if the use case are written well and there is someone that can clear some doubts.
from Albrecht's original methodology (IFPUG Function Point Analysis, and NESMA ... Is outdated and other newer methods such as 'Use Case' Points are better.