Glad,
I'll try to answer the question as best I can.
The F-35 requires some seriously high end mission planning capability. The RN has historically underestimated the facilities required to support offensive air ops, and was determined not to do so this time. The baseline designs for the QEC always had large mission planning spaces, and when the STOVL option was chosen, the large compartments on 2 deck above the aft hangar which were designed to be able to take four very large arresting engines were basically too good not to use.
At the end of the day, a primary requirement for the QEC was to be able to support high rate offensive air ops. That drove the mission planning space requirements.
Hope this helps a little, best regards to all those shuffling the spaces,
Engines