Are you sure? I was sure that the tests was made only against From field.
Yes, sure. See: http://www.openspf.org/FAQ/Envelope_from_scope
QuoteThe vast majority of SPF implementations today use the return-path as the subject of authentication and do not get involved with the header "From:".
It is either default SRS, or nothing Everything else will have strange unwanted side effects. Did I mention I hate SPF?