Gary Drescher wrote:
..

I've never felt worried about someone landing on me while I'm holding in
position at a controlled airport, but perhaps the risk is more significant
than I'm aware. Have many such collisions actually occurred?

You betcha. As a matter of fact, there IS NO POSITION AND HOLD AT
NIGHT as a result of one such crash.

We were position and holding at Dulles one day (daylight) when the
tower had to send a Gulfstream around because they realized we were
still waiting for clearance. We offered to get off (it wasn't
that close) but they declined.