Machinato Charlie

Hi everyone, my very first post: I currently work for the Department of Defense as a GS employee under FERS. I am also 80% disabled via the VA. The DAV folks have told me that if I need to retire under disability I'll receive 80% of my top three years salary for the first year of retirement and 60% for all subsequent years. The FERS material I can find on-line tells me the numbers of 60% the first year and 40% for following years. Does anybody know where I can read about this - what law citation or Code of Federal Regulations? If you don't know the site, do you know where anything is written about that difference in percentages for disabled vet employees versus non-disabled vet employees and non-vet employees? Sounds to me like, according to the Disabled American Veterans folks, I would receive 20% more than a "regular" FERS employee when I leave under disability. Well, this is a huge deal to my wife and me, but I sure can't find anything on-line discussing it. Can anyone help me out? Thank you.