My question was not about the rear window, as such. The reference that I have seen implies a cabin with a fully-glazed operating floor which did not conform to the usual SR design - I thought all SR boxes post 1930s were in effect 'ARP' designs of brick construction with small windows?
According to "The Signal Box - A Pictorial History and Guide to Designs" by the Signalling Study Group (all members of the Signalling Record Society) and published in 1986, they refer to the standard SR ARP box as an SR 'Type 14'. It was of brick construction with relatively small windows in the front and ends, from the photo of Gomshall and Shere in the book. I cannot be certain about Staines Moor box, but further information from the SRS archives* show it was a Type 14 and that the lever frame was at the back of the box, so extremely unlikely there were any windows at the rear?
*
Edit - see
Randy Ripple's link below for the appropriate page.
Your comment that an Ms. source implied windows were on all sides made me look afresh at the Historic England entry for the Grade II listed St Albans South box and that happens to describe our box as "
1st floor fully glazed with two bays of 3 lights and one bay of 2 lights: small paned sliding casement windows." yet we have a very solid wooden back wall (except where it started leaking badly earlier this year!) so I wonder if the writer of your Ms. source automatically assumed that a solid back wall would also be assumed by any reader?