you are right, what matters in the cell reselect offset is just the difference between one cell and the other.
whether CRO(A) = 30 and CRO(B) = 34
CRO(A) = 0 and CRO(B) = 4, in the end, it still means that cell B is seen 4dB stronger than cell A.
So whether you put 4dB and 8dB, or 0dB and 4dB, it will not change anything. But perhaps you missed out some cells which are set at CRO=0 dB or 2dB ?