6G networks are foreseen to improve global coverage and offer seamless connectivity toward a 6G-based Internet of Things through satellite-air-ground integrated networks (SA-GINs). Flying ad hoc networks (FANETs), based on unmanned aerial vehicles (UAVs), are an important part of SAGINs in scenarios where the deployment of conventional terrestrial networks is challenging. In this paper, we study a non-orthogonal multiple access (NOMA)-based cooperative FANET (C-FANET) in the context of propagation environments that can be represented by a semi-analytical model of the Rician K-factor. NOMA at the base station improves overall throughput while cooperative communication with UAVs acting as decode-and-forward relays improves coverage. The semi-analytical model of the Rician K-factor allows to assess the impact of frequency, number of scatterers, and radius of the scattering sphere on the outage probability and sum rate of the NOMA-based C-FANET. Numerical results are provided for a range of generic scattering environments showing options for improving system performance through the choice of frequency, transmit signal-to-noise ratio at the BS and UAVs, and receiver antenna directivity.