The roundel situation in 1.12 was a bit of a mess. A single roundel type had two different block types with different recipes: the full roundel and the 2-halves roundel. 1.16 greatly improved on this, with one roundel block that uses both the full and 2-halves textures, and adding the roundel wrench to rotate roundels. I want to add to this: a roundel block with 4 different textures; the full and 2-halves, and then two new textures: an upper single half, and a lower single half. This is to allow for new roundel patterns, for example a hexagon composed of six roundels.

An illustration of my proposal:

(apologies for the unintentionally blurry image)