The magnifications I've been using are 64X, then 90X, 127X, 153X and finally 191X (8mm) All ES, Delos or Pentax EPs.
Okay, yes, you should be able to see the rings around 127x (1mm exit pupil). It has to do with the image scale and resolution of or eye to see such things. That would be 180x in your MCT and about 200x in your C8. It could be that you did not notice them before. These rings are inevitable, they would have been present in your 180 MCT and C8, as well, at a sufficient magnification. Especially when seeing does not disturb the image appreciably.
As Dave said above, a star test would be nice. These rings are caused by two things. First is diffraction at the aperture, which is unavoidable (the obstruction is an aperture, as well...something in the light path causing additional diffraction). Second is aberration. Any flaws in the optics will exacerbate the brightness of the rings as rays (sic) of light do not focus at the same point causing some additional interference patterns. The result of this complex interference (phase) is usually light taken from the central Airy disc and transferred to the rings. So, bright rings can also mean there is some aberration.
Star testing does have a learning curve, so I do not expect one can just defocus and tell right away. Especially in MCTs due to their complex optical design. But, there are some signs that are easy to look for. One is the shadow test where we compare the size of the secondary shadow at equal distance on both sides of focus. And fairly close to focus with just a few rings visible at high magnification. If the shadow is larger outside and smaller inside (which will likely be the case to some degree), this is an indication of some amount of spherical aberration. The shadows will likely be different and may not be cause for concern, it just depends how much. A noticeable or significant difference can indicate a problem.
Another is the snap to focus test. Well corrected optics will have a certain amount of certainty when coming to focus. Poor optics will mush through focus, focus will either be uncertain or it may never focus nicely. You can check that if you wish and get a feel for how good the optics are, the more "snap" the better. If your scope is taking 191x with a nice image, I would not worry too much. No scope is perfect, some are better...but none are perfect. What really matters is how pleasing the image is at higher magnification. Good scopes can take magnification pretty well with clean images. If so, the rings are inevitable and nothing to get upset about. All scopes will show them to some degree, even a perfect refractor.