A triangle $X Y Z$ is called fun if it has the following properties:
$$\begin{aligned}
& \text { angle } Y X Z = 30 ^ { \circ } \\
& X Y = \sqrt { 3 } a \\
& Y Z = a
\end{aligned}$$
where $a$ is a constant.
For a given value of $a$, there are two distinct fun triangles $S$ and $T$, where the area of $S$ is greater than the area of $T$.
Find the ratio
area of $S$ : area of $T$