It isn't only Pazon that recommends shimming the rotor, Boyer does too...
[URL unfurl="true"]http://www.boyerbransden.com/faultfinding.html[/URL]
"On British machines, if necessary the rotor can be moved out slightly by placing a thin metal shim around the taper."
Tri-Spark instructions also say the rotor position should be checked...
[URL unfurl="true"]https://www.trispark.com.au/assets/files/TRI-0006%20Classic%20Twin%20Manual%202021.pdf[/URL]
"Step 5 - continued
Once the rotor has been fitted check that the face of the rotor is back from the ledge that the stator unit sits on by two millimetres using a straight edge as shown in the following photograph. (2mm +/- 0.6)"
...therefore, the problem seems to be with individual machines and not the ignition system, however, shimmed and still "3 to 4mm short" seems excessive.
The Pazon Sure-Fire rotor fitted to my 850 Mk3 didn't need shimming.
