I've never used Income Access before, but am currently being migrated over to them. So I have links such as:-
vendor.adsrv.eacdn .com/C.ashx?btag=a_9999b_999c_&affid=999999&siteid=9999 &adid=999&c=

Does anyone know if there is a URL parameter of any kind for setting a specific landing page?

I couldn't find any info in the IA help pages, or elsewhere.