Porsche is 14mm radius ball seat, but i suppose it is possible your lug bolt brand have less contact area due to being smaller around?
https://www.race-studs.com/products/14mm-porsche-steel-lug-nuts
There is,a thread on here somewhere that explains why not to use 1 piece lug nuts instead of the oem 2 piece design, I'll try and find it as i don't recall why.
Have you taken off one of your oem lug bolts to compare?