I agree Blyth's Reed seems unlikely. The obvious features on the wing are clear however the main sticking points are size as first described by Adrian - the shape of the head, colour of the legs, tail shape, rounded or square and was it spread out or fanned plus flicked or wagged, all points picked up by others and repeated in personal correspondence.
There is also one item I think we also have to consider and that is the bird's behaviour. On passage Upcher's are a skulking and silent passage migrant species, prefering areas of open but mixed vegetation. Olivaceous are a local migrant breeding species and behave accordingly. Quite gregarious males constantly sing often from prominent perches and all, both m/f are so much more active popping in and out, up and down and around the vegetation. They have a preference for thick mature vegetation. However Reed and Marsh warblers can be skulking or active, and when active in a feeding mode do flick wag and fan tails possibly for balance but it is behaviour seen often plus they regularly turn up in coastal halophytic vegetation especially if mixed with tamarisk as is the case in the location where AJ photographed this bird. We have ringed three or four Reed this week, I personally rule out this species with complete confidence on shape, size and colour alone even given the bad light in the pictures.
Don't know if this helps any but all adds to the picture.