The above picture, showing a 90-97 rear Koni Sport at full compression, is the reason why I include bump spacers for Konis. Due to the construction of the Koni, there is a 16mm gap in the front and 20mm gap in the rear between the shock body and the 'shelf' where the bump stop sits. The FCM bump stops both compress to about 10.5mm with full load. So a spacer of some sort is needed. Ideally the material is firm enough to resist a large compressive load but also soft enough to not scratch the shaft. That material is UHMW-PE or ultra-high molecular weight polyethylene, the material that cutting boards are made of (among many industrial uses where low-friction and high-compressive strength are needed).
Okay, so there's the explanation for 'why spacers'? There is nothing wrong with using Koni shocks with my kit - I have designed all my FCM kits to give the maximum SAFE amount of travel, and that's what you get.

Note that the factory NA bump stops are so long, even when fully compressed, that there is never a chance to bottom the Koni out - HOWEVER if you shorten the bump stops by cutting donuts off, you run the risk of blowing a shock out - there's no need to 'guess' about how much bump stop you need. My kits have all that engineered into it them.