A willow herb - but which one?

Maybe Epilobium parviflora - the small flowered willow herb?  Though that is normally found in boggy areas - whereas our garden tends to be dry except around the pond, and this isn't growing round the pond.  Certainly not the familiar rosebay willow herb with which we in the UK are all so familiar.  Early in my acquaintance with W (who came to the UK from South Africa a few years ago), he introduced me to his lovely garden, where he was growing a wonderful crop of rosebay willow herb, because it was so pretty - I suggested his neighbours might not agree when it seeded.

Anyway, there are a few examples of this willow herb in our garden.  It's been around a few years in small numbers - we pull it up if it's in the wrong place - but since it doesn't seem to be quite as invasive as the rosebay form, so I think we can let it stay at the bottom of the garden where the other uncultivated plants are allowed relatively free rein.  Elephant hawk moth caterpillars are known to favour it.