Perhaps a lighter bullet of the same caliber leaves the muzzle at a greater velocity than one of a heavier weight. That is more or less a given and that may hold the answer.
Being as the lighter projectile is moving faster from the muzzle it is less susceptible to the influences of atmosphere, wind pressure, gravity and what have you, so the flight at short range is more predictable. The heavier buller is slower and therefore more influenced by the aerodynamic factors, exaggertaing the trajectory upwards at a given distance. In this case 100-125 yards.
So when zeroing sights in for say 149gr rounds one would need to decrease the elevation for the same gun using a 182gr round to compensate for the increased wind resistance of the latter. The same applies to any gun.