Center in that example, but I think I understand your bigger question. I have on some staves in spots, started scraping away what I believed to be at that moment, proud or thick areas with the desire to get down to the ring I was chasing, only to find out that it was a thin area where I had already violated the back ring. I don't know if there is any advise I can give other than look at those areas in question very carefully in good lighting and make sure you understand the topography before you proceed.
