That may be true "IF" you use the standard rear sight like the a2 configuration, since its linked to the elevation marks, but with standard flip ups it does not really matter. If zeroed at 100 yards, the 50 yard impact is pretty much the same, and still good enough for silhouettes at closer ranges. Also if sighted at 100 yards, at 200 the irons are still on pretty close at 200 yards allowing me to easily make hits on 12" steel, thats what mine are set at. I start at 25 yards, then move to 50, and 100 for the final setting. I have sighted 30 or 40, and all of mine are set at 100. The military setting zero best I remember is 25 meters or 27 yards with the arpeture marked 0-2 or zero to 200 meter ranges.Since you are a handgunner you may not be familiar with zeroing the sights on an AR. There are several articles and YouTube videos that discuss setting your sights for practical accuracy. Here is a good article you may want to read:
Shooting Illustrated | Zero Distance for a Home-Defense AR-15
I'd just suggest doing some research before sighting in as the AR does not typically follow the traditional 100 yard zero like many folks do with a rifle.