Can you identifly

These small black flies appear each year in my garden for about 2-3 weeks.
They have very dark grey wings, almost black.
They are about 5-7mm long and spend almost all day inactive sitting on the wall of the house, they never come indoors.
As soon as you get within a few inches of them they fly off and land about 6 inches away, very reluctant to move far.

Maybe a Woodlouse fly, Rhinophoridae? They look a bit like Tachinids but are slimmer.

Thank you very much, I do believe you have found it.
It makes sense because we do get a lot of woodlice in the garden, nice to know something is attacking them to help maintain the balance.