AH Formatter / XSL Formatter
Q&A

In MathML, the default value of the lowest size of the font(scriptminsize) is 8pt. Consequently, even if you specify the size of less than 8pt for the fontsize, the size of the font becomes 8pt. This operation can be changed by setting <mstyle scriptminsize="xxxpt">.

For example.

<math ...>
  <mrow>
    <mstyle scriptminsize="2pt">
        <mtext>AA</mtext>
        ...
    </mstyle>
  </mrow>
</math>