I've played with the SMB recently on Infinite lighting and my conclusions seem to agree with your findings.  But I have noticed that lowering it too much extends the shadows significantly.  My range extended between 1.2 to 0.1.  IIRC, 0.8 SMB on infinite gave me good results with hair.  I also used a fill spotlight without any shadow; that might help with the process.  My lighting workflow with portrait images is to relatively keep it simple: one infinite for shadows, one fill spotlight and one rim light both without any shadows.