I don?t know if the above results, when compared to the results in the previous post for a1_N_1_S, do or don?t indicate that your definition of average slope is OK.
As in the a1_N_1_S case, Mean(u?) inversely correlates with LenInt.
But unlike the a1_N_1_S case, average slope ALSO inversely correlates with LenInt.
I can readily make a scientific interpretation of these two sets of results, but don?t want to do so if you think that these two sets of results indicate a problem with the definition of average slope.