I think we are misunderstanding what Rectangle.axisLat does. It gives you the latitude of a circle's intersections with its bbox meridians which I think it is not what you want. This is the intersection of the box with the circle at minLon and maxLon.
I think in your case you can use again the method Rectangle.fromPointDistance with a dummy longitude (e.g. 0.0) and use the given minLat and maxLat.