New to x-bow, have a parker buckmaster @300 fps. @20 yds. sighting dead on using 420 gr. shaft. What kinda a drop should I be lookin at 40 yds. The reason I am asking, while shooting it the other day. sighted in about 2 inches high @20 yds., using the 3rd stadia on my scope was low @ 40 yds. Signed confused.