Royal Berkshire Regt, c.1916: 9th (Reserve) or 11th (Labour) Battalion?

[DougSA]

I have just received this group photo from a relative, which features a group of what looks like men from the Royal Berkshire Regiment.

This would make sense as a 2xGreat Uncle served with the Royal Berkshire Regiment during WW1. More specifically, he was posted from Somerset LI to 9th (Reserve) Battalion, Royal Berkshire Regt, in May 1916, and then on to the 11th (Labour) Battalion, in June 1916. The 11th Bn shipped out to France in July 1916. They later converted to the Labour Corps.

Now the reverse of the photo postcard indicates that it was "Made in Britain", so assume the photo was taken before shipping out to France, which would mean during May - July 1916.

Now, I would like to figure out if it is from his time with the 9th or 11th Battalion. Would anyone have any insights regarding the war establishments of reserve battalions vs labour battalions, assuming that this may have been different? In this group, I can only see 2 officers, 12 sergeants/corporals (of whom at least 5 are sergeants), and at least 6 lance corporals (but likely more). This seems to be a small number of officers for what looks like a company sized group.

Any insights welcome!