Finally figured out why the pannier brace won't fit my bike. With the help of RPMDAKAR, we sussed out that the pannier frames on my bike had been mounted further forward than standard. Where the front fitting normally goes to the back end of the footrest, mine go to the subframe bottom joint. The upper fixings are drilled into the top of the subframe. The panniers sit further forward which, if I was ever to carry a pillion and panniers, There wouldn't be much room for the pillion's heels (unless he/she was wearing stilettos. I leave that thought with you). Hence the pannier brace, if fitted at the numberplate, has no hope of reaching forward. I'll look to do a custom job on that if I need to.
Advantage of moving panniers forward? All I can think of is a better CofG when loaded up solo, and reduce load on the subframe for a given pannier load (think cantilever force, moment-arm). Unless anyone has any other ideas? Is this a popular mod? Sorry for the murky photo.