Hello dear Rati Ray Banik

As you write above it is just an arbitrary/ reference line, and you can put them anywhere, but before that you should make a good analyze of your results, I mean you first search if there is a Wilson charge centre that can intersect this line an odd time (topological insulators) if no you can draw it anywhere.

Good luck

Thank you Mostafa Ragragui for your help.

You're welcome Rati Ray Banik.