Yes Sean all pale lower mandible (if that´s what you mean) is good for Upcher´s - and Eastern OW of course. Difficult light and view but a Hippolais it is - and the 'tail behavior' sound good and so does the broadness of the tail in the first image (not meaning that this instant view in just one image would be diagnostic for Upcher´s (the darkness of surely darker due to being in shadow as refered to by Frenchy.
As mentioned by D.I.M. Wallace for Upcher´s
'An obvious upward flick, even partial cock, developed by slight spreading of the outer tail feathers and a sideways twich (but not the full 'fan and wave' which has been described from birds in northeast Africa and the Middle East'
Also some other Upcher´s from Bahrain Bird Report 2007.