Very small black bee, the white face markings are somewhat wedge-shaped rather than linear (as in H. minisculis). It looks more like H. asperithorax on Michael Batley's hylaeine bee site.
I think you are correct with H. asperithorax. Anna. First one on CNM - I have added it to the species list. I've seen this bee at the ANBG but not been able to photograph it.