The RAF are the bombing experts and if they decided to hit that location those types of angle then I would like to believe a lot of thought went into that decision. I for one am NOT qualified to even dare disagree and I say that with the greatest of respect.
It was simple maths.
Assume that the runway is
120 feet wide and the bombs are dropped at an
interval of 0.24 seconds which equates to 144 feet. If attacking at 90 degrees it would be possible with a perfect attack not to hit the runway at all.
By attacking at an angle of
30 degrees the line over the runway would be 240 feet and you would guarantee at least one hit.
Had the stick been dropped only a quarter second earlier then there would have been two hits.