Shooting heads are meant to be attached to a straight running line made just for that purpose. Which is a fairly thin level line .... kind of like the line that is behind to front end of a WF line.....You may be attaching your shooting head to a fly line that already has a Weight forward section built into it and that probably won't work.
The shooting line is meant to be set up.... Backing - running line - shooting head - leader - fly - huge fish
hope this helps