First thing to get out of the way: I shoot a handgun with both eyes open and I
don't ascribe to the "front sight focus" method.
Here is a visual description of what you see with both eyes open, looking at the target vs. looking at the front sight:
The picture on the left shows what you do when you bowl, pitch a baseball, shoot a shotgun, shoot a rifle with a red dot, and is what you've been doing with your pointer finger since you could crawl. It's totally natural and it's what will happen, whether you want it to or not, in a SD situation, so don't fight nature, learn to use it.
Perhaps you've seen the optical illusion where you hold a paper towel tube up to one eye and your hand next to it while focusing on the wall on the other side of the room? Your brains will see an image of your hand with a hole in the middle.
It happens in reverse when you shoot pistol with a target focus - you see a ghost image of the front sight on the center of the target -- just like pointing your finger at an object across the room.
Your brain automatically knows which of the "two" front sights to line up with the target, you've been doing it since you were a baby... but just in case you have to analyze it... if you are right eye dominant the front sight on the left is the one that should line up with the center of the target. IOW the target, front sight and dominant eye are all in a line and the non-dominant eye will produce a second image which the brain (my brain anyway) ignores... hence the notion of a dominant eye.
By the way, I am left handed and right eye dominant and I shoot right handed - I've always done it, and nobody had to tell me to do it that way.