How to change phase variator timing shift

According to the Alfa documentation the phase variator shifts (advances) the intake cam timing by 25 crank degrees.
This is not what I've measured on my engine.
On my engine the variator did not have the teflon washer included in the rebuild kit. I measured a 30 degrees (15 cam degrees) shift.

However by inserting washers/shims inside the variator the shift can be adjusted to any value within a 0-30 degrees range. This is explained below.

My observation showed that the variator switches on at 1700 RPM and off at 4500 RPM. However RPM values were based on the tacho which is not precise.
Since now I've got all ECU maps I can see that two 1D maps look like activation/deactivation for the VVT. The maps define two switching ranges (to define a hysteresis): 1440-1480 RPM and 4160-4200 RPM.

Originally and without teflon washer the shift is 30 crank degrees


With the teflon washer the shift is 28 crank degrees


Every 2mm inserted between the two moving parts lowers the shift by 5 crank degrees


20 degrees shift: with a shim of 4mm


18 degrees shift: with a shim of 4mm and teflon washer