I am the wrong person to answer your question properly.....................but.
There is always a degree of error with parallax, if in theory you have your parallax set at 250 yards it is really not at 250 yards all the time, weather conditions and other factors can change parallax quite a bit.
A couple ways to manage parallax, turn down your power or have a scope with parallax adjustment.
I bought a Leupold VX-3i 4.5-14X40 a couple years ago, the model 170691 that has no parallax adjustment.....
it always has parallax issues above 10X no matter the range (btw: I Hate this scope !!!!)
I then bought the same scope with parallax adjustment model 170699 and it is fantastic.
Trying to guess where to have a fixed parallax set is futile, either lower the power or buy a scope with adjustable parallax.
