Sorting through the triangles of a NavMesh to get a single triangle from a specific area?

Okay so I undertstand how I should be doing this:

• NavMeshTriangulation.areas is an int[], each element corresponds to a triangle on the Navesh, with each int indicating the area (NavMeshTriangulation.areas[16] could be part of area 5 for example).

• NavMeshTriangulation.indices is an int[], in groups of 3 they correspond to the indices of the
  vertices (NavMeshTriangulation.indices[0] through [5] would be { 0, 1, 2, 0, 2, 3 } for a square.

• NavMeshTriangulation.vertices is a Vector3[] containing the vectors of all the verts.

So to draw a ray for each vertex of an area I would:

• Loop through the area[] to see if the index matches my area (5), store the index in a List or something.

• Loop through the indices[] (using the stored area ints to make sure I'm looking at the right triangle), store the index in another List, plus the two indexes after (to make a triangle).

• Finally use the stored values in the second list to Debug.DrawRay() the vertices.

However I've tried doing this and it keeps coming out wrong. I can draw a ray for every vertex on the NavMesh no problem, when I try and do it for a specific area it draws the rays on points other than that.

I'm probably just messing up a really silly calculation somewhere but if I do it by hand it all checks out.

Here's a very broken down version of my code that I made to make sure everything looked good: https://hatebin.com/bjrijwiveq

Thank you for any help!