Just been back through this section and found thread on Shingle Street acro, which then took me to 'Acroholics' article.
The banana posture seems to be rated quite highly in this article as indictive of Blyth's Reed, and recall the BW article on Norfolk Blyths Reed (1996?) also held it in high regard.
What is current consensus? Anybody been noting Reed Warbler in this posture? It's clear with all these Blyth's Reeds being unearthed, people are looking quite closely at acros these days.
As a 'case study', attached is photo an acro caught in the act (at Dale of Walls, Shetland mainland in late Sept). This bird caused much debate amongst our group, but in the end it seemed clear it was a Reed Warbler. One of things which threw us is that it repeatedly drooped it's wings, cocked it's tail and held it's head high.
p.s. apologies if this topic is old hat.