Hi Brian
I don't know if you are still in contact with this site. If you are, I'm not sure whether what I have to say is of any use to you. Here goes.
My father, David Morris PARRY, 102841, served in the 212 Siege Battery, RGA.
According to
www.1914-1918.net/siege-battery-index.htm this Battery was first overseas in France from 6th December 1916.
The command structure was
Y Group
Artillery Brigade (12 x 6inch Howitzers and 6 9.2 Howitzers)
The Siege Artillery Batteries were
115th, 202nd, 212th; and 218th.
all part of 68 Heavy Artillery Group.
They were fighting in the Somme sector at a place called Albert on 19th February 1917 when he was wounded. He was evacuated to the RAMC No 11 Stationary Hospital located in Rouen between 14 Oct 1916 to 19 Mar 1917. He was then shipped back to the UK.
Hope this helps. Regards Bob