It is suggested that analysis of RHEED intensity oscillations can be simplified when diffraction conditions are chosen appropriately and two cases are presented as supporting evidence. The first is an out-of-phase condition where the specular reflection from the substrate is very weak. At this condition the oscillations can be described by a kinematic calculation which is modified to take account of refraction. The second case occurs when electrons are incident at glancing angles less than about 1°. Under this condition the oscillations can have a double-minimum structure with one minimum at very small coverages of the growing layer and a second minimum at higher coverages. The minima occur because the growing layer becomes near-transparent at certain critical strengths of the laterally averaged scattering potential. This is illustrated with numerical results for lead and silver.