I don't why this category was created, but to single out the Corps of Royal Engineers from the rest of the Corps & Regiments of the British Army to me, like the Scottish Army & Navy categories, it’s a silly ill thought idea and the equivalent of creating a board for just one ship in the Royal Navy.
The Royal Engineers was original of officer corps, with the rank and file in the Corps of Artificers, later to become The Royal Sappers and Miners; all merged into the Corps of Royal Engineers in 1856.
Why stop at the RE's? There's the Royal Artillery [Field, Horse & Garrison), Royal Army Service Corps, Royal Army Medical Corps, Army Nursing Service, and each gained their Royal Prefix at different times, so what title do you use?.
In addition to the various Corps being known under different names at different times, pre-1881 there were some 109 numbered infantry regiments of foot in the British Army [some also included names in their titles] the numbered regiments reduced to around 67 after 1881; so which would you create sub-categories for and under what names?
The British Army is just that so just leave it as one single category. The only split on military boards should be around nations, service branches (Army, Navy & Air Force) and conflicts.