tex-suscript-height-minimum

tex-suscript-height-minimum is a variable defined in `tex-mode.el'.
Its value is

0.0

Documentation:
Integer or float limiting the minimum size of subscript/superscript text.
An integer is an absolute height in units of 1/10 point, a float
is a height relative to that of the default font. Zero means no minimum.

You can customize this variable.

This variable was introduced, or its default value was changed, in version 23.1 of Emacs.