Sorry to find this so late after your post. The below pic shows two regular size Provari's with both an XL and a standard length tank. I'll also add a diagram that shows what length carto to use with either tank length, which might influence which length tank to get.
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Thank you... I figured I could get a volume in ml out of someone, or at least a tank height then I could calculate the amount of juice because I know the diameter already. IBTanked FINALLY replied to my FB post and said the info was in their FAQ but I guess I didn't see it; their site is pretty convoluted. Your diagrams helped me so I think I know what to do.
I've decided to dump all my other MODs besides the Provari but I want a few atomizer options besides the Cobra. Sometimes the resistance is off, or I get a nasty burned taste suddenly, so it's easier to swap heads and vape from another one while I fix it. I have the VapeOnly BCC right now, and didn't go with the IBTanked because of the delay in their response but I think I will make a purchase from them next month anyway. I'd like a cartomizer tank to try out and I just love their fun, inexpensive designs. I already spent $160 on the Cobra so everything else, I am looking for a good buy around $15-$25, in something I can maintain/rebuild myself at minimal cost now that I have the knowhow.
19mm XL looks just fine so I think I will go with that. I can't find all the custom painted tubes they were doing however now!