Keithley 590 C-V Analyzer: Applying the Calibration Capacitor Correction

Hello,
I'm a student working with the Keithley 590 C-V Analyzer, and my testing set up is using a switching matrix and its adding about 5-20 pF in parasitic capacitance. I read the manual for the analyzer and recommended the calibration capacitor correction method. But when I apply the method the correction isn't working properly. I was wondering if there was anybody that could maybe help. I've attached the manual for reference. The calibration method is on page 247 of the pdf or 4-102 on the manual. 
Best,
Julian

Curious which test freq does your 590 have?  100KHz or 1MHz or both?
Which freq do you use?

For the calibration capacitor topic, do you have the 5907 standard caps?  Or supplying your own caps?

Are you connected through the switch when doing the cable compensation with the standard caps?
You should be if you want the method to correct for it.

You mention an unwanted offset of up to 20pF when connected through a switch.  Have you tried the zero method from section 3.10?

Your 590 is likely to be quite old.  When was last time it was calibrated?
How are you determining the value of the reference caps?

In general, I’d try evaluating just the 590 with minimal cabling to the standard caps.  If successful, then start adding in the other aspects such as the switch, etc.