I started thinking about the measurement you are probably wanting—the distance from the collar that sits against the block to the end of the CPS.
The problem is not knowing how thick the plastic is over the end of the magnet or how close the magnet is. It would seem even the strength of the magnet would affect optimal distance from flywheel and I recall the Black had a stronger magnet than the grey or purple?
I measured my (5) spare Black CPS (I did not remove them from the plastic in the event I sell them one day).
The average length is 29.00mm.
That is 29.10mm overall minus the thickness of the plastic bag (0.10mm) for a total of 29.00mm.