I've done something similar where I count the rows and do and if statement within the Condition Show option, in layout, if has too many rows, it hides the table. So if you have one dimension you might use:
Using layering, you could hide a message underneath the object the only shows when the object is hidden.
If there are 20 or less rows for DimensionA then it will show the table, otherwise hide it showing the message underneath.
Hey, Please don't forget to add kudos, like or mark as a solution if my reply has helped you at all! 🙂