To sit flush just adjust the 510 pin
(I guess)
I have the Gemini, the pin will not adjust in at all! If you try, you could break some type of connection in it, that is located inside the AFC. I haven't done that, but have read of others doing it. My advice(and what I did) use a spacer/washer. The Gemini's 510 is SO long you can use up to a 1mm spacer/washer, and it will work. You can use almost anything as a spacer, cut and old credit/debit card down to the right shape, or buy these from Kidney Puncher...
http://www.kidneypuncher.com/kp-mod-guard-5-pack/
My experience....The 22mm Gemini RTA works on the Cuboid, but doesn't sit flush...I NEVER tried to force it to...On the RX200, it screwed down fine, and wasn't forced, and I didn't feel ANY real resistance to screwing it down...BUT it didn't work correctly, the resistance would change, it would drop out of temperature control and into wattge mofe.... If I loosened it a bit, then it would work.... So, I started using washers/spacers and it works fine...Same for the Cuboid...My advice NEVER try to adjust the 510 on the Gemini, use a spacer with any Joyetech,Wismec,eLeaf mod....
Or if you have a Joyetech,Wismec,eLeaf mod, don't get the Gemini, the Griffin works just as well, no 510 pin issues, and the build quality seems a bit better. The top airflow on the Gemini doesn't do anything for me... I've tried it, but unless I REALLY crank up the power, or the temperature, it just mutes/reduces the flavor.... Since I generally use SS316L Fused Claptons, the flavor, is great, and I already use enough ejuice without cranking up the temperature, or the power.
Of note, I am speaking of the 22mm versions of both.... I did get the top airflow option for the Griffin, and tried it, but after just trying it, I don't use it, the top airflow is always closed....