The grass area is clearly part of James Clavell Square, so the extent of r15926523 is clearly too small. It's quite hard to determine the correct extent of the square, even if you've actually been there:
1) The available open data from Ordnance Survey only includes a point in OS Open Names, on the side of thee grass area and Building 45. That suggests it should be extended to the edges of Building 45 and Building 18.
2) It is not mentioned at all on the Royal Arsenal Riverside maps placed around the development by Berkeley Homes, which is unhelpful.
3) Actual street signs naming it appear to be absent.
4) Known postal addresses of premises use No 1 Street, not James Clavell Square.

I'll review it again next time I go there.