Help! Crown tank O-ring

[Acies]

I was going to replace the O-rings on my Crown. I am having a problem with the O-ring that is on the inside of the bottom piece, it's the one that touches the top of the coil when the tank is put together. The O-ring has two different sides. One side is completely flat and the other has a crevasse cut into it. My question is which side should be touching the coil? I put the flat side down. Having the other side touch my coil. Is this right?

 

[Mr. Robot]

That's right...