I'm out of inspiration...

\setupnarrower[left=.6pt,right=.6pt]

\startinteractionmenu[right]
% \startnarrower           % sets a wide right margin, whatever \setnarrower left/right settings
    \placecontent[
%        criterium=all,
        criterium=chapter,
        alternative=b,
        style=\tfx,
%        offset=5pt,                      % no effect at all
%        margin=5pt,                    % only sets left margin
%        width=.90\rightedge,        % no effect at all
%    before=\startnarrower,         % no effect at all
%    after=\stopnarrower,            % no effect at all
        interaction=all]
% \stopnarrower
\stopinteractionmenu

% \startnarrower                       % blank menu
\setupinteractionmenu[right][
%    offset=5pt,                          % no effect at all
%       width=.95\rightedge,         % no effect at all
%    before=\startnarrower,          % sets a wide right margin,
%    after=\stopnarrower,             % whatever \setnarrower left/right settings
    distance=overlay]
% \stopnarrower

Alan