MACK values differ from CDG?

[JonE]

I am noticing significant differences in valuation between the MACK values and the CDG values for my league. It looks as though top players are pretty similar, but the CDG values are consistently lower than the MACK values, and the spread generally gets wider as the values decrease. Is this true for everyone? Why is this so? I'm just trying to get a handle on how I should use these values. Thanks.