Past decades have significantly advanced our ability to probe turbulent mixing in Rayleigh–Taylor flows, in both experiments and simulations. Yet, our basic understanding remains elusive and requires better basis. For instance, observations do not substantiate the rudimentary dimensional arguments to the same degree of certainty as in classical three-dimensional turbulence. We provide a plausible scenario based on a momentum-driven model. The results presented are specific enough that they can be used to interpret experimental and numerical simulation data.