4/6 drop???

[jmcfarland67]

I know this has probably been covered a hundred times on here, but I honestly couldn't find the answer while looking through previous posts. I just got off the phone with cpp to order a disc brake with the 4/6 suspension. When I asked for the 4/6 the guy told me a c-notch was required if lowering the rear 6 inches or more. I thought I could lower 6 and not need it, unless I went lower. Can someone please clarify this for me. Thanks