I know exactly what you are talking about, not sure what goes on but every now and then I notice my shots are high. My anchor is right below my nostril and my second thumb joint against my cheek bone, hard to explain, but out of the blue, my shots are high, so I would have to adjust my aim down a few inches on target or raise my anchor to an uncomfortable/unnatural position to hit my target. Then, as suddenly as it appears, something changes and my shots are "normal" again. I am calling this phenomenon "hop up" because it reminds me of an airsoft gun hop up function. I don't feel like I changed my anchor, but none the less it's odd and weird.