if you are on a hill it might be just the top of the chunk that you have claimed. A chunk is defined by the game itself, its not like "where you stand 50m up 25m down and 15m around" there is an option to show the current chunk with a yellow border, so you know what you will claim.
Another option is to expand this claim UP so you claim the chunk above too.
if you like i can share a code snippet that lets you define a custom height. not sure how well it would work with your code.