I do not think we are ready to tighten the burnish specs. I think we need to develop more understanding of the issue first. Answering some of the following questions...Is there anything special about these interfaces? Can drive function induce the negative burnish? Is the burnish permanent? What happens to head dymanmics when large negative burnish is present and the drive trys to read or write?
Please keep digging into the problem and see what you are able to learn.