[NTG-context] no effect of \definefontfeature for adobevariablefontprototype

Hi, trying to work with variable fonts, I am stuck at the very beginning. I can't see any effect of weight parameter. Using adobevariablefontprototypebold and adobevariablefontprototypelight is working. \starttext \definefontfeature[whatever][axis={weight:150}]% \definedfont[name:adobevariablefontprototype*whatever]foo@bar \definefontfeature[whatever][axis={weight:350}]% \definedfont[name:adobevariablefontprototype*whatever]foo@bar \definefontfeature[whatever][axis={weight:550}]% \definedfont[name:adobevariablefontprototype*whatever]foo@bar \definefontfeature[whatever][axis={weight:750}]% \definedfont[name:adobevariablefontprototype*whatever]foo@bar \stoptext Can it be something from with my font file ? Thanks, Garulfo