Obviously, for long gun, the eye you use is dependent on which side the gun is mounted on. For handgun either rotate the head, or depending on your body position.
You are shooting around a barricade, which is providing cover, and you are using your non dominant hand. If you are not
cross eye dominant, you should use your non dominant eye, otherwise you will expose too much of your head to your adversary. (So if you are righty, shooting lefty, leaning lefty from behind a barricade, but you are right eye dominant - use your left eye. Of course, if you are 1/2 blind in one eye like me, then you whatever eye works.
You happen upon a situation where you immediately had to exit your cruiser, and take cover on the street, using a curb as cover, you are lying on your usual shooting side (right handed), and you are right eye dominant. The only hand available to make the shot would be your non-dominant hand. If you are right eye dominant, it would not behoove you to use your dominant eye, as again, raising your head that much to make the shot would mean more of your most important body part is exposed.
Outside of scenarios such as these (where exposure might be detrimental), I usually
advocate using the dominant eye as beatcop as outlined above.
But above all things I subscribe to the school that what tactics we use should be solely driven by the needs of the situation + our skills sets, more than anything else.
And yeah, good job on the 50 yard shot!