Generally, when a font is scaled to a lower point size, the glyphs can change to retain legibility. However, your unhappiness over the relation of the i
and m
indicates you don't like the choices made by the font.
Originally I used the scalerel
package to take a normalsize
m_i
and scale it down to an appropriate size, but then Hendrik Vogt pointed out that the same could be more simply accomplished using a \scalebox{0.6}{$m_i$}
for the sub-sub-superscript, since \usebox
does not apply the \mathpalette
wrapper.
The \scalebox
creates the subscripted m_i
to be an exact scale of the normal size m_i
. Of course, the drawback is that, when scaled down, the strokes become thinner, and some may consider that more detrimental to the appearance that the relation of the i
to the m
. In any event, here it is:
\documentclass{article}
\usepackage{mathtools}
\usepackage{amssymb}
\usepackage{graphicx}
\begin{document}
\begin{equation*}
\dim_{\mathbb{F}_{2^{%
\scalebox{0.6}{$m_i$}%
}}} W \geq \frac{n}{m_i}
\end{equation*}
\end{document}

!
in the generated markup: that will make a link to your image, someone with edit rights will put the!
back.m
in the left is smaller than them
in the right, so the output is a bit wider to enhance readability. But please don't use this sub-super-sub-superscript notation! It's not readable anyway ...