As I mentioned in my original post, in good SFP scopes, the point-of-impact shift due to zoom is controlled to about 1 MOA or less. This would be barely detectable in a normal-power hunting scope such as your 2.5-10X (It is hard to aim accurately at 2.5X and we can't tell if a shift in point of impact or group size is caused by us or by the scope or by other factors). If you have a bore sighter, you might be able to see if your scope has a shift during zoom. But even with a bore sighter the grid shown by the device is not easy to see at 2.5X. The shift in point of aim of an SFP scope -if it exist- becomes detectable only when the scope's minimum power is high, say 6X or 8X.
In summary, an SFP scope is susceptible to a shift in point of aim during zoom. This, however, is not a serious concern in good hunting scopes of nominal power.
The problem is much bigger than you have described it. The movement of the reticle is NOT linear with the zoom. Nor is it repeatable. Returning to max. power does not mean that the reticle is in the same position as before.
For long-range target shooting this may not be an issue. But for long shots on a hunt SFP scopes are a major risk if you have played with the zoom ring since the last sight-in.
Before I came aware of this issue I had a Leupold VX-6 2-12-42. With this scope I had unexplainable shifts in POI of up to 2 MOA during range sessions. I went to my smith and he put the scope in a collimator. There I could really watch the reticle wander about on altering the zoom.
SFP = never again!!
