Someone may have filed the front sight down. 4" high is about right for a 6:00 hold on a standard target. With standard sights, the 150s should be in the middle of a standard target using a 6:00 hold with 9 to 11 clicks of elevation plus a little white space, and some reduce the front sight to produce that when turned down all the way.
Take the rear sight rack off by running the sight up enough to get your thumb behind it and popping the cover off. Once loose, you will see the bottom of the rack has a segment where the teeth stop and it is solid. This is to prevent soldiers accidentally turning the sight adjustment up so high in the heat of combat that the sight comes out and they lose it. You probably don't have to worry about that, so you can actually remove the toothless segment to give yourself a few more clicks of down adjustment. Try just filing the bottom corner off of it first. I don't recall it being hardened like the base, but if your file won't touch it, a Dremel cutoff wheel will. Then put it back together and see how many more clicks down you get.
As far as grouping, many of the 147 grain 7.62 NATO BT bullets I've seen are just terribly inaccurate if that is what you have. If your muzzle erosion is at all asymmetrical, boat tails will be more sensitive to it than flat base bullets, so try some of the latter. The Hornady 150 grain boattails have worked well for me, but I know my crown is essentially perfect.