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Thanks for the extra discussion Mark and Reinoud. It seems to me that many female D. diadema do have dusting on the thorax. There are several examples, presumably reliably IDd, in the Diptera.Info gallery, for instance.

I checked the original photos for the antennae colour. They are not black, but are a dark reddish brown (darker than the leg colour). Again, it seems to me that this is more like some of the D. diadema females than the M. teutonis, which seem to consistently have bright yellowy orange antennae.

And there is jizz. In all the pictures of M. teutonis it is engaging in some sort of leg waving or posturing. D. diadema just seems to hunker down to the ground or sit up on its haunches if hunting.

I also suspect that D. diadema is maybe a bit more thermophilic than M. teutonis, but this is just a hunch. The habitat these pictures were taken in certainly seemed perfect for D. diadema. The soil is coarse sand and these flies were in some numbers.