Remember higher magnification makes everything larger, including the apparent misalignment. If you collimate at the higher magnification, then check the alignment at your lower magnification you may have a better result.
are you saying the amount of zoom changes from one eyepiece to the other? adjusting the prisms won't change that. If the alignment changes when you zoom that could mean that the lenses that are moving to cause the zooming aren't moving parallel to each other. regrettably I don't know how to fix that.
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