Ik took mine out for the first time yesterday, at 25x power the scope can't focus at 100m, you have to turn down magnification.
You run out of parallax adjustment chasing the 25x focus at 100 yards?
Try to get it in focus by adjusting the diopter a little, not so much that the reticle goes out of focus, and see if you can find a "compromise" diopter setting.
I find with some scopes (Steiner 5-25, S&B 5-25 PMII) the reticle does not snap into focus at a particular diopter setting, there is a range of diopter position within which the reticle appears focused. If this is the case with your ATACR, you may find a diopter position where the reticle is in focus AND you can get a 100 yard target in focus at 25x. I call this fine tuning the diopter.