Dear Peter,
the paper is nicely written and the results are very interesting
A few comments:
1.for the reader it would be helpful if b and d are difined in the
caption of table 2
2. as far as I understand the systematic error due to the assumption
of exponent 1 in the A dependence was not considered. Why?
3. You assume factorization in x(Feynman) and pt which usually in
hadronics does not hold (seagull effect) see e.g Z Phys C69(1995)55
This may explain the problem you discuss following formula (10).
Michael Schmelling should know all details
4. in ref PL 135B(1984)510 it was shown, that the s/u ratio in hard
processes is larger than in soft hadronic interactions. UA1 observed ~1986
a similar effect in one of their mixing papers. So perhaps your
observation is not unnatural

Necessary corrections in the references:
1. [3]Erratum -ibid B335(1990)260 missing
2. [14] misprint: 2007 Eur. J. Phys. C49(2006)545
3.[15] only K Ehret is author
4. [17] only W Gradl is author
5.should read [19] NIM A 576(2007)312
6.[23] should read R. Battiston et al ...
7.[24] I. Abt is first author of the Lumi paper -> should read
I. Abt et al arXiv...

Hope that the nice paper is published soon
Regards
Deitrich