Digital BW, The Print

Clayton (or anyone else),

I've been testing out the techniques in the variable tone article and
I've run across a problem...well, not a problem, just something I
can't think of how to adjust for.  

This example is printing Paul's step wedge.  If I set (this is an
extreme example, I know) the cyan slider to -25 and the magenta to +25
the tones in the 70-90 range are about equal and there's a clear break
to pure black around 95%.  I know there's a curve that would correct
for this (to get back to a normal step wedge) but I can't seem to wrap
my mind around what it should look like.  I should add that I don't
intend to print that way I would just like to understand what's
happening better so I can apply it to lower levels of adjustment. 

At lower slider levels I can see this beginning to happen but it's
only minimally noticeable.  

Any suggestions on a curve to try?  Also, sorry for posting so many
questions and not many answers...

Thanks,

Brian
http://www.brianchapmanphotography.com