Focus and parallax are not the same thing.
The reticle and image can both be in focus, and you can still experience several MOA worth of parallax. This applies to both fixed power and variable power optics, and the higher the magnification the greater the effects of parallax can be.
There are a million articles that explain what parallax is, and how it affects POA/POI intersection.
I’m sure that if you were to leave your scope “focused so that everything is good between 70 and 200 yards”… that you will be experiencing some parallax issues at either 200 yards or 70 yards…. or to a lesser extent, both.