I've had my X100 for a year now and hold it in exactly the same way you do. TBH, previous rangefinders I've owned over the years like the Canon QLs and Minolta Hi-Matics are exactly the same and this is where I developed the technique of right index finger inside the strap. I think it is more noticeable after having used DSLRs for so long where the larger grip means the shutter release button is further forward than the strap lugs making this a non-issue in those larger cameras. It's inescapable in the X100 and you will just get used to it after a while. An alternative would be to use some sort of strap that screws into the tripod socket, I've seen them around but can't think of a brand specifically.