Thanks for the replies chaps.
The problem is that in those two cases I am referring to, it was the ground crew that insisted on No2 to start first. In other words, they were happier to approach the inlet near the No2, than start the No1 which was literally a few feet from the airbrdge. So it is possible for No2 to start.
I was aware of the inlet geometry, I was just wondering whether there were additional reasons behind the manual's "MUST" .