This is how my mesh looks like, it doesnt matter if i add extra vertex towards the center, the material does what he wants and does not follow the vertex i applied it to like it is shown in the next picture
The subdivisions need to be supported with an extra edge loop or creasing. And that’s not a good subdivision pattern, even though it’s on a flat surface. The n-gon is concave and splitting concave polygons gives a better pattern for it.