Any gun will hit COM at ten yards...but our goal is retinal shots at that distance. Nuances in grip, how you sights, what portion of the eye you use to see the sights/dot, visual acuity, all contribute in the same way that a rifle zeroed for one man will not be perfectly zeroed for the next man.
The iron sights do in fact have to be zeroed if you want something more than point shooting at an auto shop restroom. In class I have seen new pistols with the sights off for anything more than 10 yard COM shooting. Zeroing involves adjusting them for windage and elevation with YOUR MEAT AMMO at a given distance. Most important is windage. That can be done by drifting the rear sight. Elevation is not as crucial, but that can be done by shaving small amounts off the front sight or replacing the front sight.
The zero will not be the same with Tula or WWB. I tell guys - zero for killing ammo, but note where your training ammo hits. Zeroing for training ammo and expecting all ammo to hit same is not going to happen.
Mine are set so the dot sits atop the front post when the sights are aligned properly. I find that with a ten yard zero using 115 gr. DPX ammo, I am good for face shots to 25 yards, and body shots out to 100 yards.
Once the iron sights are zeroed, simply bring the Trijicon RMR into coincidence with your iron sights and you will be zeroed. It is important to read the Trijicon manual prior to making any adjustments to the RMR unit. All the information is there for you. We suggest zeroing at 10 yards. That will give you eye socket accuracy inside 10 yards where many gunfights take place, center of mass out to about 75 yards and, using a high chest hold, allow you to hit a man out to about 150 yards.
With a 10 yard zero and 115 grain DPX ammo this is what it should be for bullet drop per JBM Ballistic Calculator.
0...... - 0.7
5...... - 0.3
So...out to 100 yards you are within 6" point of aim vs point of impact and with less drop at 100 yards, than other zero distances. Look at these charts.
10 yard zero
25 yards is +0.7
50 yards is +0.4
75 yards is -1.9
100 yards is -6.4
15 yard zero
25 yards is +0.2
50 yards is -0.6
75 yards is -3.4
100 yards is -8.3
25 yard zero
25 yards is +0.0
50 yards is -1.0
75 yards is -4.0
100 yards is -9.1
Another reason to zero at 10 yards in the accuracy of pistols in general. From a rest with factory ammo the best you are going to get group wise is 3-4" at 25 yards. This can be frustrating as you will be chasing zero around to get it centered in the group.
I have mine at 10 yards. I can put five in an eyeball...literally a 3/4" paster dot...at that distance. It is the farthest "long shot" inside my home. Yet with the Corbon ammo, it will still allow for face shots at 25 yards, and body shots at 100 yards.