Keep your coils closer to the posts, 2.5 shouldn't be an issue at all, I just built the one I bought for $5 from vaporworld with 3mm .24G 8 wrap SS, and it fits fine, had to keep the coils a little high, but its fine. 2.5mm with round wire should be a breeze, thicker wire or exotics may need to be dropped to 2mm.