QTR-Quadtone RIP

The documentation that I've read gives and unclear explanation of how
to choose the ink calibration limit. 

In one document it says that it should be around step 50 because you
just want the whole square covered, and that when you add inks later
on you don't want too much laid down. But in another doc (Moore's
User's Guide) it says something like he chose 85 because that's where
he got the max density on the wedge.

I'm using a 3800 and looking at the existing profile fore Enhanced
Matte neutral the ink limit appears to be set to 50. On my printer
when printing the ink separation wedge I get dmax of 1.74 around 70%
when the ink calibration slider is at 100. With the 50% patch giving a
density of 1.64. If I set my ink calibration limit to 50 and then
re-print the separation wedge my dmax is 1.68 at 100%. 

Does this make sense? Shouldn't I be striving to get the best dmax
possible by moving the ink calibrtaion limit up to around 70%?

Thanks, Derek