A researcher estimates a population mean using a stratified random sample. The population is divided into $H$ strata. If the variance of the mean estimator $\bar{y}_{st}$ is given by $V(\bar{y}_{st}) = \sum_{h=1}^H W_h^2 \frac{S_h^2}{n_h} (1 - f_h)$, which allocation strategy results in $n_h$ being proportional to $N_h S_h$?