Need help with 8388 ready to run distributor

Just installed about 400 dollars worth of 8388 ready to run dist.The problem is it puts to much timing in it.20 degrees at 15" of vac.So if your at 36 degrees at cruise it will be 56 degrees with vac.I was told by jegs it would only add 10 at 15" of vac.I wanted to run it on constant vac and add around 10 at most and these canisters are not adjustable.Anyone have this problem and what did you do other than unhook it