Thank you @ChrisL, this is very helpful !
Yes, the 8.7% does make sense, however I did notice that they use 2 different formulas to calculate the amount you have to pay and the amount used as basis to determine the ‘IK-Eintrag’.
So, taking a fortune of 2 millions (W=40), our yearly contribution would be:
V = 159*(40-13) + 106 = 4'399 CHF
On the other hand, the value V used to calculate the ‘IK-Eintrag’ is lower:
V = 130.50*(40-13) + 87 = 3'610.5 CHF
This corresponds to a fictive yearly income:
I = 3'610.5/0.087 + 0.5 = 41'500.5 CHF
I don’t know the reasons behind this but it is nonetheless very interesting to run more accurate simulations.
[edit] I see that the result above is matching with the document pointed out by @xorfish in the document linked in this post