\usemodule[x][asciimath]

\setupmathfraction[i:frac] [mathstyle=small]  % was script

\starttext

    $1^{1 \frac {3} {4} }$

    $\frac {1^{1 \frac {3} {4} }} {x^{\frac {1} {2}}}$

    \asciimath{1^(1 3/4) / x^(1/2)}

    \asciimath{1^(1 3/4) / 1^(1/2)}

\stoptext

