topo index

[Dan Riker]

Hello there,
I am still trying to determine the topographic index ln(a/tanB) and i do have some values.  they seem to me to be strange, in that there is a bimodal distribution, with peaks at 17 and 0, while the lows are at 21(the highest value) and 13.  Is this a common thing for rugged topography?
If not, any suggestions as to what I am doing wrong?
I think that it would really help if i had an example set of data, so if anyone could supply it I would be most appreciative.
Thanks,
Dan Riker
Duke University