The vertical directionality of an averaged acoustic field is shown in theory to depend on the depth at which it is observed in a special way. The result is based on a simple angle transformation, and is limited by the assumption that the field is a superposition of independent plane‐wave components which obey Snell’s law for a stratified medium near the receiver location. The approach applies to both transmission loss and ambient noise, and is used to derive a relationship between the directionality at a single depth and the depth dependence of the total (omnidirectional) intensity. Examples show the influence of the local sound–speed profile and illustrate sensitivities in the relationship for special cases. Implications for measurement strategies, data interpretation, and predictive modeling are discussed.