Try creating an Enterprise Field, set it to equal Baseline Finish, and roll
down to the assignment level. Republish and see if that works.
Note that on some pre-SP2 environments, I have had an issue where once a
formula is set, the roll down option is not available. The work around,
best I can tell in that scenario, is to upgrade, or to add a macro to Project
to copy the data in the file, then publish.