Hello @fyrst.z, like Zed said, the gland nuts definitely are specific to the struts, and you should use the Koni gland nuts. If you have one side of the front that threads and the other side that doesn't, that definitely could be, also as Zed said, decades of dirt and oil that create a "spacer" down there, so check that as well. The only other options would be non-matching strut cartridge heights, which will be fairly easy to check, or damaged/modified/mismatching strut housings. Struts, whether Tokico, KYB, Koni, are different heights, and they all have different gland nuts to go with them. You show an image of a strut installed with what looks like a KYB gland nut, we assume you are not using those gland nuts on the Koni's.
When you're certain there isn't a buildup to scrape out of the bottom of the housing tubes (it isn't easy, unfortunately), and if then using the Koni gland nuts you are not able to torque them down to a 4mm gap, regardless of side, just give our sales technicians a call at (800)633-6331 or (714)639-2620, or email if you prefer at info@motorsportauto.com, and we'll get things figured out.