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This is Coenia - I think palustris, but difficult to be certain. It looks like the lower picture may be a male, in which case it's not curvicauda (which has very large genitalia), and the pale haltere also suggests palustris.
You may be confusing the presutural supra-alar with a postpronotal bristle - there should be a short (though still quite strong) postpronotal, if I remember correctly.
I have found that palustris tends to have bronze-green reflections whereas curvicauda has purple-bronze reflections, but this is not in itself a good character to use.
Cranefly can tell us whether vulgata is easily separated from these two, but I don't think it occurs in Denmark.