When doing inline math I see that the mathsize does adapt when \tfa, \tfb, etc are used, but not for \tfx and \tfxx. That seems strange to me, because in the manual in the font table \tfx \tfxx \tfa etc. are advertised as equivalent operations. It also accounts for a lot more typing (and mistakes).
Why is the behaviour different? And if it is not on purpose, can it be remedied then?
A minimal example:
\starttext
{\tfc tfc 123 and \$ tfc: $123$ \$}\crlf
{\tfb tfb 123 and \$ tfb: $123$ \$}\crlf
{\tfa tfa 123 and \$ tfa: $123$ \$}\crlf
{normal 123 en \$ normal: $123$ \$}\crlf
{\tfx tfx 123 and \$ not tfx: $123$ \$}\crlf % math does not adapt size
{\tfx tfx 123 and \$ again tfx: $\tfx 123$ \$}\crlf
{\tfxx tfxx 123 and \$ not tfxx: $123$ \$}\crlf % math does not adapt size
{\tfxx tfxx 123 and \$ again tfxx: $123$ \$}\crlf
% the next does work as expected:
\def\smallsize{\switchtobodyfont[9pt]}
{\smallsize smallsize 123 and \$ smallsize: $123$ \$}\crlf