Thank you @mesquitebean and @fanfare and @CatinaT1 , very helpful, and this completely explains why it's there. This is the first year I've really checked with to this level of detail, and I was really doing it while helping out my daughter with her return (she was running into the classic AGI mismatch during online filing error, the one that's solved by entering 0 instead of the AGI).
For my issue, now I know how it works, so this will help for years to come. I appreciate it!
