The red dots have the dot focused in the distance, so you have to do the opposite of iron sights, focus your eye on the target and the red dot will be focused in front of it.
The red dot works off geometry and parallax, that is why it can acquire target so much faster than iron sights. You simply put the red dot on the target, it can be anywhere in the window, as long as its on the target the pistol is line up (if its zeroed in properly) no line up with other sights necessary. For at target less than 7 yards and putting the red dot on the edges of the window, error comes into play and it could be a little off. If your shooting targets close up, keep the red dot near the center of the window.
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Basically, the curve of the window reflects the dot projected on it, so that it will line up properly with the target, regardless of where you line your eye up in the window. But I have found you get a little off if you put the dot on the edges of the window.
You can practice at home, the muscle memory of raising the pistol level enough with the red dot to the eye level to acquire the red dot quickly over the target. At first I spent a lot of time hunting for the red dot each time I raised the pistol, after a little practice at home and developing some muscle memory, I can easily acquire the red dot right away.
In fact I have found the medium sized windowed red dots, like the RMR with a little practice I can acquire the red dot just as fast as the bigger windowed red dots like the DeltaPoint Pro and Sig Romeo 1 Pro, making the bigger window only result in getting in the way.
Remember, the arrows on the red dot are for moving the dot to the point of impact, usually 1/4 MOA. So if your hitting left of the point of aim, you want to turn the knob in the direction of right. It just takes one time reversing that in your head and adjusting the opposite to screw you up and it will be two more range visits before you get it back to close to accurate.
I have three red dots, actually 5 now, but the other two are for my 1911 80% frame projects that I am finishing the cerakoting yet to be mounted when the job is all done.
2 of the three, came with suppressor height sights from the factory that are perfect for co-witnessing with the smaller red dots.
So my FN FNX-45 Tactical with Trijicon RMR, the factory suppressor height sights were very accurate and co-witness with this red dot perfectly.
I simply started by adjusting the red dot to line up with the iron sights as I co-witnessed with them. After that is very minor, one or two click adjustments.
My SA XD-M Elite OSP with a Vortex OPMOD Viper, the factory suppressor height sights were very accurate and co-witness with this red dot perfectly.
I simply started by adjusting the red dot to line up with the iron sights as I co-witnessed with them. After that is very minor, one or two click adjustments.
No my Sig P320 M-18, the rear sight is in the optics plate and I mounted a DeltaPoint Pro on it, since it was designed for the delta point pro. The delta point pro is too big to be able to co-witness with suppressor height sights. I did get some sights big enough to co-witness, but they were not a matched set and they shoot high. I had a heck of a time zeroing the Deltapoint pro because of this.
Since the Romeo 1 Pro and Deltapoint Pro are so alike, this is likely your problem as well.
What I did to finally get it down, was get a rubber block bench rest and shoot from 7 yards out, just the red dot, forget the iron sights and co-witness, they were unreliable. I finally got it zeroed in and started walking out the distance of the target to adjust finer.