On His Post, At His Post

I have this:

link
On 21-22 April 1914, while leading three picket launches admist heavy enemy fire, McCloy was wounded but remained on his post, enabling cruisers to save American lives. For his gallant heroism, he was awarded his second Medal of Honor.

For heroism in leading 3 picket launches along Vera Cruz sea front, drawing Mexican fire and enabling cruisers to save our men on shore, 22 April 1914. Though wounded he gallantly remained at his post.

Is one of "at his post" or "on his post" wrong? Or are they both the same?

Solution 1:

"At his post" is commonly used to refer to the task currently assigned to someone. "Despite heavy enemy fire, the soldier stayed at his post".

"In his post" is commonly used to refer to a long-term rôle or position. "Despite scandal and heavy criticism, the minister stayed in his post".

"On his post" can be found used for each of these. It's found more for the latter than the former, and it's found much less often than either.

It strikes me as wrong, though as J.R. points out, prepositions do often overlap in in meaning. I'd recommend favouring at because it's more often used and is distinct from the in sense, but I wouldn't go so far as to call on incorrect.