Well, to start off, because you made a change in the parallax setting, does not necessarily mean that is the reason for other changes, so don't automatically over look other posibilities.
That being said.
Mostly, the calibrations on the parallax of a scope do NOT directly correspond the actual ranges.
This is something that you must test and verify. Then keep a cheat sheet for the adjustments on your regular tracking range notes.
Also... you must always adjust the parallax from the same direction, because the tracking forks have play in them. I can't speak to the Zeiss, but Leupolds must be adjusted from the larger distance to the shorter distance ALWAYS!!
That means if you want to go from 100 yds to 500 yds, you must go to the end (past infinity) then back to 500... if you want to go from 500 to 100, you can go directly from 500 to 100, but not the other way around.
For a Zeiss, you should test it and determine which direction the play comes into effect.
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