I’m no expert on (regular) astigmatism, but I think it would be expected to manifest as spherical blur when the cylinder correction is wrong. I tried to explain (my understanding of) it on the wiki page
The focus is smeared out along the line of sight, rather than a single point, so there’s myopic directional blur in one axis, and hyperopic directional blur in the orthogonal axis, giving a net circular sort of blur. As cylinder correction is changed towards the optional value, the amount of blur reduces.
It manifests as directional blur only when the object is too distant to keep the “circle of least confusion” (?) on the retina.