Testing closure models for the TOMs $\overline{w^2\theta }$ and $\overline{w{\theta }^2}$ with data of a 3D RHD simulation of envelope convection in a DA white dwarf. The same models as those given in Figs. 1 and 3 are used here. The case of the TOM $\overline{w^2\theta }$ is shown in the top row for the full vertical range (left) and for the upper half of the domain (right). For the line style and colour coding, see Fig. 3. The bottom row repeats this comparison for $\overline{w{\theta }^2}$. A discussion of the results is given in the main text.