Yes, you use the " little Notch at the bottom of the buckhorn" to align the front sight in! And, manufacturers typically put HIGH front sights on their guns, particularly those with fixed height rear sights, so that you can FILE down the front sight to bring the POI up to your POA with a good load you develop FIRST. What this means is you first work on developing a load that groups well. When you are satisfied with the velocity and group size, then you file the sight down to " zero" that load to strike center at a given distance, or range.
For Instance, my .50 caliber rifle is zeroed to shoot a .490 RB using a .015" thick patch, 2 inches hight at 50 yards, and 1 inch low at 100 yards. I use 65 grains of FFg powder for the shorter range, and 75-80 grains for the longer range " hunting " load. When developing the load for the gun I was concerned with accuracy FIRST, and speed and trajectory second. You can learn to hold over for longer shots, because you won't have to hold over much. I do not intend to shoot any game at distances over 100 yards with the gun. Its a round ball gun only. It will not shoot conicals.
To get that sights to " zero", I filed and test fired my gun at the range for several hours, before I had removed enough of the front sight to bring the POI up to where I wanted the ball to hit on target. That is the fun of shooting black powder. The entire process MAKES YOU learn everything about your gun, and you become much for used to shooting it, than other rifles you may own, as a result.