The zone for the SRB is based upon active service; indefinite reenlistments are required for SSG and above with 10 or more years of totalserive.
I might be able to give you an idea of the calculations when I get back to the office monday. Honestly, the SRB confuses the hell out of us. I helped a soldier with an indef reup almost a year ago and I still have no idea (after 3 pay inquiries) how his bonus was calculated.