Digital BW, The Print

I'm using QTR on my 1160 with UT inks on Epson Heavyweight Matte.
Although the density of the darkest K patch on the calibration target
was 1.73 the density measured at 100% of the 21 step wedge after
calibration only comes to 1.65.

I picked 80% as a default ink limit. I seems that I should be able to
achieve at least 1.70 which was the density of 80% patch on the
calibration target.

Should I keep poking around or are here other forces at play :) ?

Thanks in advance,

Roman