Back to swirlies -- I *think* to get them to happen with any regularity, you need to have a background (or foreground) that is far enough away from the PoF to allow the coma to form a recognisable oof projection, but not so far away the shape blurs into oblivion.
Here is a shot where I attempted to induce it with a lens I own known to exhibit a small amount of coma. I was only mildly successful, but I think (hope) it's enough to illustrate my point. Also if you look at the speculars in the background, you can see the oval shapes and even tell they occur at 90 degrees to the central axis of the lens:
Cheers,
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