Well, I am going to ask a question that might seem ignorant but I just want to clarify my calculations because as KingANuthin posted above these ballistics are not much better than a bow and arrow. When the ballistics calculator asks for the sight height it is referring to the distance between the center of the muzzle and the top of the front sight, correct?
Typically......yes. Your line of sight is an imaginary line between the rear sight, front sight to your target. This is a straight line in relation to the bore or axis of your barrel.
Bullets do behave just like a bow and arrow or vice versa. Gravity is constantly pulling your projectile back down to earth.
The speed and angle at which your projectile is launched versus the resistence it encounters will depend on where it falls back to earth.
Your velocity is measured in feet-per-second (FPS) and the ballistic coefficient deals with how well the bullet reacts with the resistence of air and gravity.
Sectional Density tells you the performance as far as penetration along with bullet design.
It's when your projectile meets your line of sight that your gun is "zeroed"
Whether you "zero" at 100yds, 200, 300 or more or set your sights for an approximation thru several ranges as MPBR, knowing where your particular bullet is going to be at all ranges gives you a leg up when shooting a target.
If you want a flatter trajectory change to a different cartridge. 7.62x39 is not a great cartridge for ballistics, it's comparable to the 30-30 with pointy bullets.