Default Position DFF based on Job EFF on Promote and Change Position

Client is trying to built a Business Rule to default Position DFF fields based on Job EFF (Legislative Info) on Promote and Change Position page.
We are not able to fetch Job EFFs to the expression. Is there any limitation that we can not use Jobs' EFFs in the position DFF default value?

Has anyone succeeded in fetching EFF values?

Any advice or hint would be appreciated