The main reason for this problem is that the carbine dove tail was made for the type 1 rear sight and not the adjustable ones. The flip sight had plenty of room in the dove tail to be moved in what ever direction it needed to be for the carbine to be sighted in. The adjustable rear sights have a much larger base that can over hang both sides of the dove tail. The sight can only move so far to the left before it hangs off the the side of the dove tail as it's so big. When the adjustable rear sights were added later on, no one sighted them in before they were staked in place so there is only a little bit of adjustment available and in some cases it's not enough. While carbines are not fragile, 60 years of use and abuse have taken a toll on many of them and they just don't shoot like they used to.