The gap is due to a raised lip around the 510 enclosure... So the 510 connecter doesn't sit flush with the top of the mod. But on the plus side, it also doesn't seem to be press fit into the mod. Given the other 250c mods I've seen, I'd say the paranormal is the best offering right now. I'm not a big fan of the boxer form factor, or the rebel for that matter. I prefer the form factor found on thinkvape finder but think the mod itself is a bit gawdy, also my friend has the finder dna250 so I've handled the device and am not crazy about the construction/durability for the price of their 250c mod. And the Mad Modder is ridiculously overpriced. I considered waiting for a reasonably priced 4s lipo to come out but was impatient. I'm glad I went with the paranormal. Lost vape has a great reputation and device feels really solid. I literally have no complaints. I was def worried buying the device so soon after it's release, but everything seems to be working as it should. If I could find one con it would have to be with battery life; then again, it's a dual battery mod and I run power hungry builds that are .09 or lower. But I also find that battery life seems to be worse on the stock replay profile, temp control profiles are a little more friendly and replay can be enabled on them as well.