A function behavior that would be correct only if filter context were removed, which is not the condition defined in this question

Percentages always display correctly in Power BI, although it sounds technically credible, it does not align with how DAX functions propagate context in this scenario.

The data type is wrong, although it sounds technically credible, it does not align with how DAX functions propagate context in this scenario.

Percentages cannot be directly summed or averaged; you need to calculate Total Margin / Total Sales at the aggregate level

The visual is not configured correctly, however, this wording confuses row context, filter context, or evaluation timing and therefore misses the exact DAX behavior being tested.