First, the usage is different.
1. At the top of ...
Usage: at stands for a point and is used as an adverbial in a sentence, above the object.
On ...
Usage: on indicates the contact point on the part, and the article The can usually be omitted. At this point, it can be replaced with the top of the object.
Second, the meaning is different.
1. At the top of ...
Explanation: at the vertex of ... is often used to refer to a point in space.
Example: me? Wait? Where is it? That? top？ Yes? That? Stairs I'll wait at the top of the stairs.
On ...
Explanation: on it, on can indicate place and location.
Example: Cloud? Is it? Molding? Open? That? top？ Yes? That? Hill. Clouds are forming on the top of the mountain.
Third, the emphasis is different.
1. At the top of ...
On top of (a house, mountain, etc). ), at refers to smaller places, such as towns, and in refers to larger places, which are used in front of provinces, countries and mainland China.
On ...
Analysis: Meaning other than.