Sounds strange. Haven't had much experience with carto
tanks and none with the iatty on the p18, but my ody works perfectly on my p18 and my p10 ( looks a little weird on the p10). I mention the P10 because I know that the center pins on my Precises aren't at the same depth. I use a mark t infinity atty on my p10 with no problems but on my p18 I have to use a spacer to get connection. That being said, the odys adjustable center pin is a great help when dialing in my perfect draw. I adjust the center pin about 1/16" out past the threads and tighten it down to the point where it makes connection. From there, I am able to tighten for a "stiffer" draw, and loosen for a "looser" draw. I'm able to do this with the ody on both mods. As for carto tanks, I used a liquinator for a couple of weeks without any draw issues. Actually, by using the "slidey" nature of a carto tank in combination with the flat top of the p18 I was able to control the liquid flow from the tank to the carto (very effectively) and the air draw to some extent. I would hold the tank tightly to the top of the p18 and take a "little toot" to get the juices flowing and then slide the tank up slowly to adjust the draw. This method worked very well for me, I just don't like the taste of cartos.
As far as I'm aware, you can't adjust the pin on your precise. But I do know that David will do It for you if you send it to him.
Sorry for the long post, I hate to witness someone not getting the most from the P18. It really is a great mod, good luck!!!!