Hi Christian,
I have been thinking about your question. I don't recommend defining a Line Item Dimension in your example with GTIN/EANUPC. The Dimension Table contains 8,000 distinct values, which is "only" 0.4% of the Fact Table (24 million records). Why should you use in such cases a Line Item Dimension?
The classical example of a Line Item Dimension is Document No. Such a Dimension can potentially grow direction 100% of the Fact Table. A Line Item Dimension can be considered if it becomes more than 10 - 20% of the Fact Table. But still be careful and try first other options to remodel the Dimensions. Otherwise it could work contra-productive and might even lead to performance degradation.
Best regards,
Sander