Hi @Ofer_Cohen!
You could try to add additional CASE around the calculation to perform it only when the Issue level is Epic:
CASE [Issue].CurrentHierarchy.Level.Name
WHEN 'Epic'
THEN -- previous formula here
END
If this does not help, please export the report definition and send it to support@eazybi.com to see what other report configuration could be improved.
Lauma / support@eazybi.com