Kirchoff's law doesn't say which direction it emits in. As shaped charges can alter the direction of where the blast wave goes, I suspect an analogous behavior of a heat shield can direct where the emissions go. I.e. as you say, an asymmetric shape.

PS I haven't done thermo in nearly 50 years!

V-groove radiators are a really neat, unintuitive design, which gets strong directionality out of thermal radiation. It's the thermal design SPHEREX went with—the space telescope that went up a few weeks ago, that was all over HN.

That's: a cavity that's a thin wedge in between two slightly angled plates, where the interior surface coating is partly emissive, and partly infrared-reflective—it can reflect the thermal radiation it emits. That means specular reflections, following geometric optics, so it works like a horn for light—beams it out the sides in a narrow cone.

(.pdf) https://ttu-ir.tdl.org/server/api/core/bitstreams/71aee1e9-3...