Interesting. All of mine hit the back. I always thought that was meant to push the cartridge in and secure it there. The neck may be tight but a long cartridge can't possibly move. Eg I notice Lamys are sold with a removable ring that stops you fully tightening the barrel by accident and breaking the seal of the cartridge that come's with the pen. I don't see why designers would choose not to secure their proprietary cartridge like that, unless they want to be able to design shorter models and use the same cartridges.