Thanks, duegatti. I didn't do a search - my bad. From the illustrations on the configurator it appears to be sloped from the front towards the front wheels so it may effectively be less than PASM. 10 mm is about what PASM adds (or subtracts) uniformly.
10mm it is, even for me with S-pasm and Sport Design i dont have any problems.
Its also how to define -10mm, you loose 10mm at the front but the plastic things in front of the wheel arch (dont know the English Word) goes way lower then the front.
And that part is the same with or with out Sport design.
Here you can se the part i talk about, in front of the front wheel, 20" rims on this Picture.
According to the manual link above the ground clearance of the 718 (measured at the lowest point in front of the front wheel arch I presume) is 112-113mm (assuming SPASM -20mm) up to 131-133mm (base suspension no PASM)
According to GregW in the thread linked above, his yellow 718 base Boxster with base suspension with regular front apron has the front tip of his regular front apron 7" (178mm) above the ground (he also noted that this point was 33 inches forward from where the front wheels touch the ground)
Since you have a Cayman S with SPASM and Sport Design Apron, that *should* make your front apron tip 148mm above the ground. (assuming -20mm drop from SPASM, and -10mm because of the front apron shape). If it is not... then we can calculate the exact value the sports apron changes things!
I don't know why I care so much, since my car is already built and I can't change the specs now... but I'm just very curious.