Jeff, I have two early model 20" ACD monitors attached to my PC, and until I had a good quality profile made for a new (and better) printer, thought the calibration was OK. Like you, I was finding the monitor was a little cool though I didn't have the contrast issue you mention. I also use the Monaco Optix XR puck, and I was using the XR Pro software. I view my prints under 6500k diffuse lighting.
After many unsuccessful recalibration attempts with the Monaco software (couldn't get it very much nearer the output) I switched the profiling software to basICColor display 4.0 (after also testing ColorEyes), profiled to 6500k rather than 'native' to a target luminance of 120. I now get a much more accurate match to my output. I don't have the measurements to hand, but I recall that my monitors' native white point was around 5700. The basICColor profiling software simply gave me a better profile almost straight away. Are you profiling to native? Have you tried switching the white point?
I'm at a loss to understand though why you're only seeing this issue with 6x17 scans - I'd have thought that if your monitor calibration is out, then it would be out for everything...?