6-o'clock works great so long as you're allways shooting at the same size bull, and allways from the same distance. Otherwize, you're gonna miss 'cause the gun aint shooting where the front sight is looking.
On the other hand, center is allways center, no matter what size the target is....squirrel, rabbit, deer, pig, man, Coke can or oil drum....it's all the same.
I guess that what I'm getting at is that I aint smart enough to use a 6-o'clock hold for "sighting in" a weapon. Heck, I have enough trouble figuring distance, wind and bullet drop as it is.....let alone trying to do all of that with a gun that was "zero'ed" to shoot way-high to start with.
At any rate, getting back to the OP.......yeah, some guns do shoot high with their factory-supplied sighting arrangement. Ruger SA's are famous for that, and there aint but three things that can be done about it:
1) Raise the front.
2) Lower the rear.
3) Develop some sort of "specialty load" just for that one gun.
Me personaly, I much prefer lowering the rear, especialy if I'm going to use said gun for anything other than a range toy. Reason is, the other two have drawbacks of their own which I'd rather not deal with unless I just had to.....so....that's what I'd try first.
But that's just me.
DGW