crossbow question

[mokap]

I have a excalibur phoenix and have the varizone scope on it and im having trouble.Its sighted in perfect at 20 and 30 yards but out to 40 and fifty yards the arrows drop 4-5 inches short.im using field points and i have a rangefinder so i know the yardage is right.whats the problem???or should i just sight it in at 2-3 inches high at 20 yrds or something like that?somebody please help me.

[Dnk]

If your crosshairs are dead on at 20 then holding your crosshairs on center shoot a group at 50 and then turn your speed ring until your 50 yard mark on the scope intersects with the 50 yard group.

[mokap]

so do i turn it to a higher speed number or down.and i do this until my 50 and 40yard mark is hitting where its suppose to?and it wont effect my other aiming points?sorry im a little confused.

[smokepolehall]

turn your speed ring to slower fps that will raise the impact at 50 yds and leaves your 20 yard sight-in as it is