at a guess, 5 is the size, but they change over time(patchs, etc), or is the dl size with the 7.2 the full unpacked and installed size, with the 16 gigs needed to download, unpack, and install-basicly, the min. amount it will allocate so as to make sure it dosnt run out of room while working on it before it removes the extra when its done.

I think the total space required ends up quite high because it includes the two expansions.

So it's something along the lines of..

FEAR -5GB
Extraction Point -2GB
Perseus Mandate -7GB