I posted a similar question a few days ago and somebody was able to help me. Hopefully this helps you as well!
Go to my profile and find the post titled "Adjustable Reference Line Based on Filters"
Try rewriting it as below and see if it works:
Note: Ensure that your Plant Region is added to Context, just as I have added the Region to Context here. A sample workbook is attached.
That is exactly I want.
Glad it helped Have a nice day