Sorry, linear mts is the exact expression from RN site not lane mts., and in engineering linear mts is for length, then to calculate area mts you multiply by the width, and the width is not something fixed, it is not 2 always, it is what is required by the particular engineering, 2 mts. or 3 mts or 4 or 1 mt.
Note that if it would be fixed for 2 mts. always, as you or wiki say or interpret, then would give the amount of 2400 sq mts for vehicle deck parking area in Bay which contradicts with 24 Challenger 2 tanks, or contradicts with size of Bay compared to Cavour´s hangar 2500 sq mts, or Canberra´s hangar 3000 sq mts, contradicts with the length and width of those ships compared.
Finally my guess is what you mean, reduce Galicia dock and increase with that or little more from wherever in dimensions to get 1200 sq mts. in Bay, if they referr just to vehicle deck with that.
"The flight deck can accommodate two Merlin or Chinook helicopters, and a hanger could be fitted in future if required"