QTR-Quadtone RIP

I am in the process of running the ink limitation procedure and am having difficulty 
determining the first patch in the 21 step tablet "where it appears that all the paper is 
covered with ink". It seems to me when trying to follow that guidline that there is too 
much room for interpretation. My determinations can be all over the lot. 

Can anyone suggest a more precise guideline? Also how do you choose the ink limit to use 
if you get widely varying results for the different ink channels? 

Any suggestions will be appreciated.

Howard