How does scatteredInterpolant extrapolation choose triangle?

Hello, this is a question I've had for awhile, and has popped up again so I'd like to ask how linear extrapolation really works for scattered interpolant. My understanding is that the linear extrapolation is still based on barycentric weighting - extrapolation means that there will be negative weights. That's fine for me. (If it's wrong, I may still be interested in knowing how to do this).

What I don't know is how Matlab identifies which three points, i.e. triangle, to use for query points outside of all triangles. Nearest triangle center is computationally easy, but doesn't always give the expected result, which I suppose is something associated with its dual voronoi diagram... Does anyone know how scatteredInterpolant actually handles this?