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.