Theory and Application of solubility Parameters are beyond our scope. However, an interesting viewer should have at least read through collection of research by Charles M. Hansen, published during 60s (Ref.1). One of the parameters discussed in this book is Hildebrand solubility parameter ($\delta$), which is a good indication of solubility, according to Wikipedia. The principal utility of Hildebrand solubility parameter is that it provides simple predictions of phase equilibrium, based on a single parameter. These predictions are often useful, particularly for nonpolar and slightly polar systems without hydrogen bonding. According to the tabulated $\delta$ values, ethanol is polar, and has relatively higher value ($\pu {12.92 cal^{\frac{1}{2}}cm^{\frac{3}{2}}}$) than that of hexane ($\pu {7.24 cal^{\frac{1}{2}}cm^{\frac{3}{2}}}$) (Ref.1). Yet, it is interesting to note that hexane is soluble in absolute ethanol, but is insoluble in methanol ($\delta_{\ce{MeOH}}=\pu {14.28 cal^{\frac{1}{2}}cm^{\frac{3}{2}}}$), albeit the difference of relevant Hildebrand solubility parameters (${\Delta\delta}$) is just $\pu {1.36 cal^{\frac{1}{2}}cm^{\frac{3}{2}}}$ (from Ref.1 and 2).
It is an interesting aspect of the Hildebrand solvent parameters that the $\delta$ value of a solvent mixture can be determined by averaging the $\delta$ values of the individual solvents by volume. For example, if you mix $V_\mathrm{A}$ of solvent A with $V_\mathrm{B}$ of solvent B, the mixture will have Hildebrand value of $\delta_\mathrm{Mix}$, which would be given by:
$$\delta_\mathrm{Mix} = \delta_\mathrm{A}\left( \frac{V_\mathrm{A}}{ V_\mathrm{A}+ V_\mathrm{B}}\right) + \delta_\mathrm{B}\left( \frac{V_\mathrm{B}}{ V_\mathrm{A}+ V_\mathrm{B}}\right)$$
Let's see what is the $\delta$ of 96% ethanol ($\delta_{\ce{H2O}}=\pu {23.5 cal^{\frac{1}{2}}cm^{\frac{3}{2}}}$):
$$ 23.5\left(\frac{4}{100}\right) + 12.92\left(\frac{96}{100}\right) = 13.34 = \delta_{96\%\ce{EtOH}} \lt \delta_{\ce{MeOH}}$$
Let's see now, what is the value of $\delta$ of 90% ethanol:
$$ 23.5\left(\frac{10}{100}\right) + 12.92\left(\frac{90}{100}\right) = 14.0 = \delta_{90\%\ce{EtOH}} \lt \delta_{\ce{MeOH}}$$
Even though still $\delta_{90\%\ce{EtOH}} \lt \delta_{\ce{MeOH}}$, the concept is clear. The value is more than $\delta_{\ce{EtOH}}$ and getting closer by each addition of water droplet and to been not miscible with hexane. Therefore, it is safe to say that these data would gives you some insight to what you are looking for.
Note: For a review of solution systems: See ref.3
References:
- C. M. Hansen, In The Three Dimensional Solubility Parameter and Solvent Diffusion Coefficient: Their Importance in Surface Coating Formulation; Danish Technical Press: Copenhagen, Denmark, 1967.
- C. M. Hansen, "The Three Dimensional Solubility Parameter Key to Paint Component Affinities: 1. Solvents Plasticizers, Polymers, and Resins," Journal of Paint Technology 1967, 39(505), 104-117.
- R. Wiśniewski, E. Śmieszek, E. Kamińska, " Three-dimensional solubility parameters: simple and effective determination of compatibility regions," Progress in Organic Coatings 1995, 26(2-4), 265-274 (https://doi.org/10.1016/0300-9440(96)81583-9).
