Isometric Rule Tile - Rotation/Mirror is useless for non-square tiles?

I have a project set up which uses your typical 2:1 ratio of isometric tiles. I was setting up an isometric rule tile using the latest 2D Extras package for 2019.4 and noticed that the rules for rotation are useless for that ratio (not a huge surprise), but also that mirroring does not behave as expected at all.

The mirroring clearly shows an icon for a left-right or up-down mirroring, but it's not behaving that way. Instead it's acting as if the tile is rotated like a standard non-isometric tile. For example, let's say you made a sprite meant for a top corner, and set up the mirror Y rule on it/. Instead of your top corner being also used for the bottom corner, it mirrors to the right instead.

I can get around this by quadrupling the artwork, but I'd rather find some way to use the Isometric Rule Tile's rules to save me the trouble. Also curious why they made this decision, as the only way it'd look good is if the isometric style was a 1:1 ratio.

Here's a visual. Green arrow shows the tile in its correct unmirrored spot. Blue arrow shows where I expected it to go when mirrored. Red arrow is where the mirrored version actually ended up.

 

Sorry the delay, my account wasn't set to send email notifications for replies, so missed your response.

Here's the relevant sprite (it's pure white, so a little hard to see on the checker pattern of the editor) from the sprite editor, showing the pivot.