X-ray standing waves has been used to determine the structure of over 15 two dimensional graphene-like films (e.g. graphene, boron nitride, silicene, transition metal dichalcogenides). This work has provided the beginnings of insight into how these 2D films interact with their growth substrates from films that basically free-standing on the growth substrate [1], to those that are effectively alloyed with it [2]. Much of this work has been performed in close collaboration with theoretical collaborators. However, due to often small mismatches between the lattice parameters of the substrate and the two dimensional film, the overlayer unit cell can be quite large and, in some cases, non-unique. This problem can quickly become intractable for accurate density functional theory (DFT) calculations. As a result, much of the simulations present in the literature are for artificially strained  overlayer unit cells [3,4,5], but this may be an unhelpful approximation for many two dimensional films [5]. In this talk I will introduce the X-ray standing waves measurements that have been performed for these films, discussing the variation in results that have been observed and how they have been interpreted. I will then address the performance DFT calculations to precisely model these structures, with a focus on the limitations of these  overlayer unit cells and the need to perform fuller, more expensive calculations to gain meaningful results.