Hi Sylvain,

you can avoid this with the following code (althought the "height"
option is probably not needed):

  \setuplayout[width=middle, height=middle]

I’m not expert on typesetting, but I read somewhere (too long ago to be
able to remember when) that printed papers should have wider outer
margins to put your fingers on it.

See the following the output from:

  \setuppagenumbering[alternative=doublesided]
  \starttext \showframe \showsetups \stoptext

Just in case it helps,