AF080C Ring Flash exposure problems

I bought an AF080C flash almost a year ago now for some macro work with my Ds. The TTL works proficiently for the intended macro work, generally producing accurate exposures, however I also intended to use the flash as a fill-in for portraiture and these images always yield underexposed images.

I know that the TTL is based for macro (because of its low guide no.) but I would have hoped it would adjust itself accordingly for fill in when the subject is further away ie for a portrait.
The only method I have managed to get a half decent shot is to set the ringflash on full manual and set the camera to manual and keep adjusting the aperture.

I really like the effect of using ring flash for portraits and have tried it with a canon 1ds and it works fantastically well with their ring flash. The photographer Rankin used it throughout his Australia trip www.rankin.co.uk so you can see how the ring flash looks with portraiture.
Any help would be greatly appreciated

The 80c is not very powerful, but to see whether it is the lack of power or something else to blame, try experimenting with everything set to manual.

For posed portraits, the light is usually pretty steady, and there is little benefit to automation.

G