GRA, even though that isn’t Kyle’s way, many are limited by range policy or rules and are forced to make modifications to the zero process. In truth, there are many ways to skin a cat. That being said, the way they recommend will will work just fine. Now that you have shot it at 25 yards and have adjusted your sights to where the round (projectile) impacts 1.5 inches below your point of aim, it is time to confirm that at 100 yards. At 100 yards, shoot some 5 round groups and then make any fine tuning adjustments to your sights to get you where your round impacts the target at the point of aim with your iron sight or optic.
Do it the same way for optics.
I hope that helps.