Grid co-ordinates on an irregular surface

Hi all,
I’m having difficulty keeping consistency between starting points for lists on an irregular site. Point in curve and cull pattern is almost working, but I would like to keep the leftmost column in keeping with the rest of the grid - it should be starting at five here.
I have been trying to resolve this by taking the culled points in the grid and replacing them with null values, but I’m not sure how to then rework them into the overall grid pattern. Does anyone have any ideas?
Thank you.

I think this post Reorganize point structure is very similar to your case. You just want to offset indexes so that they align with the correct row (right?)

Thanks for the quick reply - I’ve taken a look at the solution you provided there and I am still unclear as to how I translate this when working with a rectangular grid as I’m not looking for any closest points nor dealing with brep projections. Surely all I have to do here is find a way to keep the point structure of the whole grid while also removing the external points? Apologies, I’m not great with tree data.

site (13.6 KB)