M Theory Lesson 274
$m_1 : m_2 : m_3 = c^4 : c^2 : 1$
where $c$ is a characteristic GUT coupling. This expression should be familiar to AF readers, at least in the context of MUB operations.
Recall that a $3 \times 3$ symmetric matrix is the sum of a symmetric 1-circulant and a 2-circulant, which is automatically symmetric. Thus a symmetric matrix $M$ with first row $(c^2 , c, 1)$ may be expressed as where the second factor is itself a sum of circulants. This makes explicit the contribution from dimension $2$ that we see in the Fourier decompositions for the mixing matrices. Vafa's (neutrino) Yukawa matrix is just of this form for $a=0$ and $c$ a cubed root of unity.