% the small one is always virtual, the 'normal' one comes from the front

\startbuffer
    \startTEXpage[offset=10pt]
        $ a_{\actuarial{n}} \quad a_{\,\actuarial{n}} \quad a_{\smallactuarial{n}}$
    \stopTEXpage
\stopbuffer

\starttext
                                \getbuffer
    \setupbodyfont[palatino]    \getbuffer
    \setupbodyfont[cambria]     \getbuffer
    \setupbodyfont[xits]        \getbuffer
\stoptext
