Theres actually no concern for critical measurement here. The recess on the film holder is simply too shallow to accommodate the ridge on the Graflok back. To visualize this, stack two books on a table and the lay another book with one end atop the stacked books and the other end on the table. You get one end elevated preventing a flush mating of the face of the book and the table. Thats all thats happening here. Once that is corrected, it is the whole face of the film back that registers the film plane (which does match all other "graflok" back style roll film holders). This is simply an instance where the shallowness of the recess causes the left side of the film holder to be higher and not flush against the graflok back. Once the ridge is filed down, the holder will lay flush (if the theory is correct). The film plane would automatically register correctly once the mating is corrected.