Bembidion obtusum

My biggest challenge identifying this species has been getting it to the correct genus, thanks to some confusion about whether or not the sutural striae is recurved. I've had the same problem with other Bembidion, but it seems more marked in obtusum than the others I've found so far. Although worded slightly differently in each key, both Hackston and Duff separate genus Ocys from most other genera in the tribe by it having the sutural striae recurved at the elytral apex. Indeed this is the only character used in Duff's key to genera. As far as I can tell, these obtusum have the sutural striae continuing round the apex of the elytra and curving back, which is what I thought was meant by recurved striae, so that should then make them Ocys. But none of the Ocys fit, and I'm now satisfied that they can't be Ocys. In my earlier days of beetling I identified an Ocys species (unaware that the species I identified it as was quite rare in Norfolk). Looking at the photo now it looks like a Bembidion species, not Ocys, and I presume I went wrong because of this.

Once I'd moved past the couplet for Ocys the first individual here keyed straightforwardly to Bembidion obtusum.

Bembidion obtusum showing elytral apex and rounded hind angles of the pronotum, North Elmham (Norfolk, UK), 28th January 2023

This one was slightly trickier as on the right side of the pronotum the side margin was very slightly sinuate just before the hind angle (though it was more rounded on the left side). Treating it as sinuate it keys to nigricorne but as well as there only being three records of that in Norfolk, other characters don't really match up - so I think it's safe to say it's obtusum.

Bembidion obtusum showing elytral apex and hind angles of the pronotum (including a close-up of the right-hand corner), North Elmham (Norfolk, UK), 28th January 2023

Again on this one I think the sides of the pronotum just before the hind angles are slightly sinuate. Taking them to be sinuate (bearing in mind that the key stresses that this may need to be looked for carefully, which implies that even the slightest sinuation counts) it would key to nigricorne. But it looks like obtusum, and I presume that's what it is. Incidentally, several photos of obtusum online show the same shape - maybe I'm just misinterpreting what sinuate (when it has to be looked for carefully) means? If you draw a tangent to the edge of the pronotum at about 9/10 the line (green dotted line shown below) cuts the hind angles off because the edge curves slightly outwards again immediately before the corner - doesn't that mean it's sinuate?

Bembidion obtusum showing close-up of pronotum, North Elmham (Norfolk, UK), 29th March 2023

Bembidion obtusum showing hind angles of pronotum, Wendling Beck Environment Project (Norfolk, UK), 1st to 4th March 2023

Bembidion obtusum, North Elmham (Norfolk, UK), 20th February 2018