comerade,
You must have seen the DVD I did years ago on basic accuracy techniques. I haven't done any more videos, but the major point for your question is the scope height above the bore affects longer-range zero, the reason the 25-yard zero doesn't work as well anymore, since the scope height above the barrel has generally increased with larger scopes.
I published an article on why the 25-yard sight-in doesn't work nearly as well as it used to a while ago, which with additions became a chapter in my 2014 book, MODERN HUNTING OPTICS, available through riflesandrecipes,com. That chapter provides far more information than I can summarize here.
