Thank you for the update. That was a good move! The map can be compared with the trench map of the time:
https://maps.nls.uk/geo/explore/#zoom=15&lat=50.87131&lon=2.90887&layers=101464903&b=1 (use the blue slider button to reveal the present day satellite image).
As you've seen from the diary, the entry on the 21st only mentions the wounding of the battery commander although the shelling on the 20th is recorded.
Precisely where 56 Battery was is not straightforward to determine. The annotation "Wilson Farm" earlier was the position of the brigade headquarters from 8th August which then withdrew to "near Vlamertinghe" on 11th. The batteries used the guns of 174 Brigade from 8th to 11th and then "went forward to man their own guns". Apart from the personnel of 56 Battery coming out of the line for 24 hours rest on 16/17 Aug, there was no other movement up to the time of his death.
Unfortunately 174 Brigade’s diary for Jul to Sep 1917 is missing! The controlling headquarters at the time records the handovers and take overs but doesn’t record where they were!
Going back further, on 1 August the diary records each battery moving one section to advanced positions in [what was formerly] No Mans Land, You have to go back to 12 July to find 56 Battery (and others) moving to positions “one and a half miles north of Ypres”. The sum total of all of that is that on 20/21 August all one can say is that the batteries were split with positions in the Wilson farm area and another position further forward. All fairly typical for artillery deployments at the time of intense activity.
Whatever, I’m glad you got something out of the diaries and the maps. Note though that Ypres was a long way from the Somme! This was the 3rd Battle of Ypres, also to become known as Passchendaele.
MaxD