QTR-Quadtone RIP

I'm posting this thinking this may be of use to other newbies like me.

Today was the first time I tried to use QTR to characterize and do 
curves and got some seemingly strange results.  I'm using the Windows 
version on an Epson 4000. In doing my Hardware Ink Limit with Moab 
Kayenta paper, Black maxed at 65% (density = 1.61 with an Eye One 
spectro) then decreased after that; 100%=1.49. I duplicated results 
with a second sheet of paper. Checked this on H Photo Rag and Moab 
Entrada, same pattern of maxing out around 65%, then decreasing.
Cyan maxed at 95%, Magenta 85%, Yellow 85%, the three light inks at 
100%.

So I have two immediate questions: 
1.  Is this non-linear pattern supposed to happen?  
2. What should I use for my Ink Limit?  I assume it should be based on 
the full strength inks, not the light versions, but even with these I 
get a range from 65%-95%.  Tom Moore's user guide says the the ink 
limit value is not critical, but which one to use....?

I used the 65% value and forged on.  My first test with the 21 step 
tablet showed the same non linear density pattern. Max black (1.60) was 
55-65%, density decreased both below and above that range.

Again, is this supposed to happen or am I doing something wrong.  

Thanks,

Bob