The formal energy‐flux solution for range‐averaged level in a varying duct depends on the definition of transmission loss, on the local impedances, and in a complicated way on the vertical angles and cross‐track variations. But for most purposes a very simple low angle version is sufficiently accurate and well established to be virtually independent of the detailed profile. Surprisingly, the convergence factor with circular symmetry is also independent of the detailed profile; this is true for unbounded media as well. Depth transforms are presented for the angular distributions of intensity, initially without specific reference to sources. Angular distributions for discrete sources show some characteristic zeros and infinities. It is shown that only the Gaussian distribution is self‐reproducing with changes in depth. The law of conjugate depths states that intensities will be equal at such depths, and it is expected that this law will be very robust. Work on these and allied energy‐flux methods is reviewed.