As far as I recollect, it was built to that size and not with a view to enlarge it.
This really is in the distant past but I remember steelwork being erected where the main body ran approximately where the airside frontage of the cargo terminal is and then at either end it was angled at 45 degree angles. This structure was never finished and was around for a good year or two and maybe more than that before it was taken down. It was quite narrow but had a large frontage. One of the wings was located where London Aviation was before that structure was itself knocked down to provide a new home for Harrods.
What I am struggling to remember was whether London Aviation was built after the steelwork was taken down or whether London Aviation's hangar was a part conversion of the angled wing.
I wish I had taken a photo of the abandoned steelwork as I have never seen a photo of it.