[NTG-context] Simple font size changes command

Dear all, In a simple document using only 1 font but with different sizes what are the easiest switch commands to change font size locally ? I am aware of \tfa, \tfx etc …. but they do not seem to size in absolute size but rather relatively to current font size. In the following MWE : \starttext {\tfd Foo {\tfx Bar1}} {\tfx Bar2} Baz. \stoptext Bar1 is typeset much larger than Bar2. I’d look to write something like but don’t know who to get \BigSize and \SmallSize defined (and have Bar1 and Bar2 of same size) : {\BigSize Foo {\SmallSize Bar1}} {\SmallSize Bar2} Baz. Many thanks for any hint. Best regards Joseph Canedo