[NTG-context] interline spacing, me too

Hi, please look at the attachment. I want different interline spacing for big, normal and small font sizes. What is the best approach? I tried \setupinterlinespace[big] (works only after \starttext!) or \setupinterlinespace[line=3.5ex] (works also before \starttext) but this changes, as intended, interline spacing as a whole. There is also \setupbodyfontenvironment (Problem with \chapter{…} or did I something wrong?). Now I've to use \switchtobodyfont[…] instead of \tfa and so on. Is there a trick? Thank you in advance Andreas