Thanks for all your answers.

just don't justify:

\setuphead[align=flushleft]

I realized I did not do my homework so well (I certainly had to get up too early). My \sectionhead parameters were already setup with : align={lohi,flushleft,nothyphenated,verytolerant} Maybe my margins are a bit too tight!

\setuphead[section][align={flushleft,nothyphenated,broad}]

or

\setuphead[section][align={normal,nothyphenated,verytolerant,extremestretch}]

Adding extremestretch did the job. Thanks a lot!

You don't need \usetypescriptfile when the name of the typescript and typeface are the same because \setupbodyfont loads the file on its own.

Good to know. Thanks! Damien