Was he waiting for me at or on the top of the stairs

Question

Doing a grammar test I was to choose between on the top and at the top in the sentence:

He was waiting for me ___ the top of the stairs in his pyjamas.

Had it been the top of the staircase, I might have chosen the first option without thinking. But stairs, not the top stair of the staircase, made me doubtful. In the long run, I chose the "at", which appeared to be the wrong choice. Trying to find out why, I gave up after an hour of browsing.

Could anyone kindly try to explain this to silly old me? If the difference between the two is so essencial to the test-makers, is it not less essencial in the spoken language?

BTW, sure thing, I didn't miss a relating post here, but it didn't help me with those top stairs, not mounting tops.

Answer 1

I'm not sure what is proper, but in everyday speaking I've never heard "on" in that context.

While thinking about it a bit, I moved his position:

He was waiting for me on the bottom of the stairs.

Which doesn't sound right, but also doesn't really tell me where he is. I'd almost expect him to be stuck under the staircase like a sticker.

Thinking and researching a bit more, it seems the target indicates which to use, and the rules are pretty vaguely defined. The answers to this question seem to suggest that has to do with the distinction between and surface and an upright target, which I think I agree with (the examples given there might not show that, however, because in that context they also show a difference in intent vs. final resting place)

So, to compliment our "at the top of the stairs" example:

He was waiting for me on the second floor

The expiration date is printed on the top of the jar (I'd expect it to be on the lid)

The expiration date is printed at the top of the jar (I'd expect it to be on the jar itself, near the top)

He was waiting for me on top of the house

He was waiting for me on the roof

Note that at is often used to be more specific about the position/location of the subject.

He was waiting for me at the top of the ladder

He was waiting for me on the ladder.

In the last one, we know he is on the ladder, but we don't know which rung he is at.