Something I didn't think to mention in my earlier post is that, at least for me, when using a rifle scope (with magnification) with both eyes open the eye looking through the scope becomes the "dominant" eye.
That's really user-specific. I can't force my dominant eye not to be dominant without closing or covering it. Everyone is wired a little different. My son is the same way. My brother is the same way. My daughter is the outlier, and she is more like what you describe than she is like me. It's really an individual thing, and to some extent (again individual) you may be able to "train" yourself. But not everyone can.
