A loop & merge doesn’t have to be based on a question.  You can add the scenarios directly to the loop & merge fields.

@TomG Thanks! Is there a website/link that I can find out how to add the scenarios directly to the loop & merge fields? 
Also, there should be 24 observations for each participant if I repeat the same 4 questions for 6 short cases in Qualtrics, right?
Thanks a lot! This is really helpful!

Thanks! Is there a website/link that I can find out how to add the scenarios directly to the loop & merge fields? 

Here is the Loop & Merge Fields section of the support page.

Also, there should be 24 observations for each participant if I repeat the same 4 questions for 6 short cases in Qualtrics, right?

Yes, you would have 4 questions in the loop & merge block and 6 loops (rows) in the loop & merge setup.