Originally Posted by mekanik ➡️

The waveguides disperse energy from the tweeter over a larger area. The reason for the odd shape is that this waveguide is most likely not designed to have equal dispersion/radiation pattern up/down as left/right or perhaps something else.

Waveguide design is complex. And they don't all look the same since they are designed for different tweeters, and for different goals. What do you want to achieve?

They come out looking weird if the simulation software deciedes that that is the shape required for that specific wanted dispersion/other characteristics.

Btw I'm quite sure that last one is not a waveguide at all, it a horn.