Reflection coefficients have complicated variations with incidence angle which can be calculated once the densities and velocities are set.
Conservation of energy is automatically satisfied when the boundary conditions are imposed.
Hence the name 'Zoeppritz equations'. The equations give the solution for the case of an incident wave of amplitude 1, and the amplitudes of the generated waves are Rpp, Rps, Tpp, Tps, and a complete description also requires knowing Rss, Rsp, Tsp, Tss 2. One cannot generally write down a simple form for the reflection and transmission coefficients, except for special cases, but these are worth remembering. Here I is the acoustic impedance, the product of P velocity and density for layer 1 or layer 2. Important boundaries can be essentially invisible at near offsets, but produce large reflections at far, and vice versa.