I ended up using 3 dished on my ducabike slipper to get it right. My STM required 0 to get it right. It's trial and error.....
You may want to make a cuppa and get a sandwich..... https://www.ducatiforum.co.uk/threads/clutch-questions.51479/
I have seen a few things regarding slipper and some say don't be surprised if stack height gets close to the edge. I will only go up in 0.5mm increments
Ps, on both mine, the 1.5mm steel were actually 1.4 and the 3mm friction nearer 2.9. A tiny amount but multiply over a stack.....
Ahhhhh I see well I am lucky my steel plates are either 1.5 or 2mm I have used a vernia on them and the friction plates are new and all measured 3mm