My belief is that the income tax effect approaches zero.
I agree with the rest of your post. There is no way of calculating an effect from the CNIT since there is no theory that explains how it is a cost. This has been one of my concerns here.
The effect cannot be quantified....but it is undoubtedly exerting an influence over the price of the goods in the world market. For a scholarly view of the incidence of taxation.....please see:
Stephen J. Entin, TAX INCIDENCE, TAX BURDEN, AND TAX SHIFTING:WHO REALLY PAYS THE TAX?, Institute for the Research of the Economics of Taxation, Policy Bulletin No. 88, September 10, 2004, at: ftp://ftp.iret.org/pub/BLTN-88.PDF