I think your results with the leaves are consistent with what I read from the book sometime before. They say that NearIR waves contains more energy , hence, deeper penetration distance compared to MidIR. The good side is that the reflecting signal contains richer info of the sample, i.e., a few cm below the sample’s surface. The downside is that it may pass through very thin sample, i.e., leaves.
That’s what I think 😉