With all due respect David, your numbers seem odd. The 9 inches on the fringe I can see, but 6 foot putt down hill? The flag-stick is more then 2 yards from the fringe on that hole. If you meant 6 yards, I would've used a value of 60 with 40% power. The caddy would have probably given a 60 value too.
Sting brings up a very good point. Sometimes the ball shows it lies on the fringe, but in all actuality, it's in the rough, or the other way around. Also, we can't forget the VEM factor, or shot randomness.
Changing the putting scale to a higher value works for me every-time, even sometimes using the caddies suggestion. I have to say I've only whiffed a few fringe putts and it was early-on in 2010. I also have a good example of a fringe putt saved on my profile too.
I wouldn't give-up on it David. Maybe try some practice fringe putts to get a feel for the higher putting value.