I disagree. Anyone who knows me has seen me shoot about 5 different guns. A Seitz, Alfermann, SuperX-1, 870, and a Blaser. The only gun I struggle with is the high rib unsingle Blaser, and on a previous thread, many agreed that they could not shoot a high rib unsingle.
For some it is crossfiring/cross dominance, but there are many reasons why the brain and your eyes do weird things with the sight picture on various targets. Concentration should increase success, not hamper it. And if you have to train your self to shoot a certain gun, you'd best sell it, adjust your POI, or get it fit properly.
Either way, it is a non-dominant eye/brain issue, but not necessarliy cross firing.