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I see that you have posted a similar photo in the past:
https://diptera.info/forum/viewthread.php?thread_id=29897

I am not an expert but it is known that size of flies can vary based upon availability of food. For example, Pollenia rudis can measure between 6 and 10mm. If a 10mm male meets a 6mm female, then you have a strange photo. Perhaps this is a case of a smaller female meeting a larger male.