The reason for 50yds...80% of engagements take place at and well under that range.
Actually, the reason is that due to the height of the sights over the bore, and the ballistic curve, if adjusted for 0 at 25 yards, the bullet is about 4" high at 100 yds, and about 6" high at 200 yds. It is back at zero at 300 yds.
BUT if you zero it at 50 yds, you are only 1.7" high at 100 yds, zero at 200 yds, and -3" at 250 yds. Even at 300 yds, you are only about 6" low. So, the result is you are +2" to -3" out to 250 yds. Not bad!
The "Santose Zero" is superior at the most likely ranges of engagement, and still works farther out.
The results are slightly different for a carbine length sight radius, but if you will zero at 50 yds, it is still quite good.
4 cm is a little much, you want better than than. You want a near cloverleaf at 50 yds.