It is interesting how everyone's experiences vary with the Project X. I love it.
Currently I have one X setup with a 32x3/40g 316L twisted fused clapton and another with a 26/36 316L clapton. Both wick and vape excellently with great flavor. No problems. I honestly do not think the X is finicky with coils but that is only my experience. Every wire type I've thrown at the X performs very nicely for me.
The way you described your experience with fused claptons leads me to suspect you are using too much wick. The wick was too tight inside the coil. From my experience "real tight" wicking will lead to the exact problems you are experiencing. When you say "real tight" I have no way of knowing exactly what you mean without actually seeing it for myself up close and personal. My mind automagically goes to "that's likely too much". Your "real tight" might be my "just right" ... I don't know.
The basics of wicking for all atty's is simply ... too tight will lead to dry hits/burnt cotton AND too loose will lead to flooding/leaks. You knew that though!!!
When installing a wick, on any atty, there should be
some resistance felt in your fingers as you move the wick side-to-side in the coil. Not too much. If your wick is moving freely then there is too little wick. If it is moving the coil and warping its shape then that is too much. I find "just right" to be when the coil moves very slightly from side-to-side with some resistance. With any thinner wire type, like 28g or smaller, you may have to hold the coil in place with a fingernail as you pull the wick through to avoid warping the coil shape.
With cotton I personally like the wick to have slightly more, or a tad more, within the coil. Overall thickness. With rayon you do need to use ~1/3 more, give or take, versus cotton. There is a balance that once found is the sweet spot (cotton or rayon).
Every wire type I've used in the X has worked well for me. I am able to get a great vape and excellent flavor from whatever coil type I install in it. Doesn't matter if it's plain kanthal, simple round 316L or a clapton. Also, for me, it doesn't matter if I am using cotton or Tidi rayon ... I am able to get a great vape.
In the following photo (prior to dry burn) I have a spaced 26/36 316L clapton 2.5ID 6 wrap coil that comes in at 0.45Ω (LV wire I linked a page back). Note the coil is secured on the insides of the screws. With a coil this size, and spacing, securing it to the inner sides works nicely and retains my desired spacing. If my coil was 8 wraps I would have slightly increased the spacing and secured it to the outer sides of the screws. Is it best, or better, to secure on one side or the other? No, not at all, doesn't matter IMO. I secure based on coil size only and have done it both ways ... the X still vapes great either way.
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Coil spacing ... does it matter? Here we are likely getting rather nitpicky. I am not a fan of widely spaced coil wraps because I don't feel they perform well - my opinion only - doesn't make it wrong or right. My preference is for the wraps to be more closely spaced/tighter. In all the coil photo's I've seen it appears to me that more closely spaced wraps are the general consensus. I've made coils with wider spacing and for me they don't perform as well as a tighter spaced coil does. I've seen explanations for this but can't find that in a quickie search ATM.
I've also used plain kanthal setup as a contact coil, or non-spaced, in the X and it vapes nicely with excellent flavor. For me personally I am able to use any wire type and get great flavor. Some swear by this and that wire type but honestly it all comes down to whatever works for each person is the correct, and best, route for that person. Maybe I'm just lucky with being able to use many wire types. I don't think so but who knows. Also I am not real fussy with having to use this or that in order to get a great vape/flavor. I like to switch things up, a lot.
In the end for any RTA it all comes down to wicking. Wicking is where the art lies ... IMO. Anyone can be taught to roll up a good coil.
I don't know if you have more than one Project X or not. But if you do have 2 ... and are willing to send one to me I will set it up with either a 32x3/40g 316L twisted fused clapton or a 26/36 316L clapton, or clapton wire you send, test it and then return it to you so you can see how I did it, vape it and check it out and see what you think. Just a thought. Let me know and we can go from there.
Wowza ... this got long!!! Apologies