Hello, I'm using your plugin on Maker MZ.
It's a very nice plugin.
If you use a large character chip, the reflections will be reversed on the right and left.
I'm trying on a new project. The version of MZ is 1.4.4.
Can you confirm it?
Thank you.

Hello and thanks for the comments.
Looking at your screenshot, I can guess that you use a big character sheet set like default (4 big monsters on the sheet, one per line, all facing down), isn't it?
The plugin expect a 4 direction sheet. For big character sheets, that means a single monster per sheet facing the 4 directions.
If you don't use 4 directions for your big monsters, then simply copy paste the same big monsters on the 4 lines of the sheet.
EDIT: I think you could also use the comment tag <fix mirror image> so it will reflect the image as is...
Regards.