Two-dimensional (2D) or single-layer materials consisting of ultra-thin films of one or few atomic or molecular layers with a crystalline structure present a broad range of unique properties such as extremely high strength, electron mobility, thermal conductivity, remarkable optical characteristics, etc.. 2D materials are thus the objects of extensive research aiming for applications in numerous domains such as flexible, nano-and optoelectronics, biomedicine, energy storage, and plasmonics. X-ray reflectivity (XRR) is vastly used to study surfaces and interfaces of hard and soft condensed matter materials, including 2D materials, nanomaterials, and biological systems. It allows deriving the laterally averaged electron density profile of a material surface region along its normal with sub-Angstrom precision. This allows determining parameters including surface roughness, structures of a single layer or multilayered materials, and the effect of capillary waves on liquid surfaces. High-brilliance synchrotron X-ray beam allows resolving materials structure at molecular levels in real-time under environmental conditions, hardly accessible to other surface-sensitive experimental techniques. Examples of such experiments are investigations of liquid surfaces and interfaces, using dedicated equipment and sample cells. However, a particular issue exists related to the XRR from liquids. The wetting angle between the liquid and the support induces a curvature to the sample liquid, which generally complicates the data analysis. This issue can be tackled by utilizing sample environments capable of working with large area samples, e.g., Langmuir trough, applying special data treatment methods, or using X-ray nanobeams . However, in some cases, the sample curvature can be exploited advantageously, e.g., Festersen et al. used a wide parallel synchrotron beam to record XRR curves in 'one-shot' but limited in the range of scattering vector q.