You are not including enough parameters in the relationship. It is too simplistic. And the more you add the more feculent it becomes. Even the measurements of output impedence are largely irrelevent, as it is an active i.e. dynamic process that is frequency and amplitude dependent, and so is your cable relationship. Measuring DC is pretty pointless, BUT I am not going to get into an endless argument about it. Something that just keeps re-occuring means that to someone for some reason being right is important. So be right and be important.

Richard