You should post this on the HYDROCAD forum. There are many experienced users as well as the software developer Peter Smart who can respond to you question.
HYDROCAD is a very intuitive program and is very reasonably priced. I can't imagine paying the ridiculous price for the Haestad product! HydraFlow is fine, but once you use HYDROCAD its hard to go back to anything else.
Unfotunately our local plan reviewers use HEC-1 to check all detention...