How to describe "circular area" in CVLGrid with low orthogonal deviation?

I met a water body like a circle(Fig.1). I don’t know how to correctly draw curvilinear grid? Because if I draw four lines surrounding the circle, the orthogonal deviation is higher than accepted limitation “3 degree”(Fig.2). I have “Orthogonize Global”. What should I do? I checked the tutorial video(here) but its example is about river, whose shape is a rectangular.
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