IMHO--I don't have the science to back this up, but it's my conclusion on my personal experiences....that each rifle has a unique BC due to variances in stability and groove/bore signature the rifle's barrel imparts on the bullet. So your results in the field vs the computed by your ballistic solution CAN vary (and very likely will).
Have you "track checked" your rifle scope yet? You may find that more/less elevation is being applied to your reticle than is indicated by your turrent.
A yard stick at 100 yds, with the rifle locked into a vice, and then manipulate the elevation turrent to the 960 yd solution, and see if your scope is applying the assumed solution.
If you hang the yard stick level with a plumb line, you can verify your optic isn't introducing any "windage" into your elevation only solution as well, during this same range session.