I find that the placement of an equation number makes a difference on the amount of white after the equation. Should they both give the same amount of whitespace? Or is the difference intentional? But then why?
I add a minimal example.

Hans van der Meer

% Test white after formula with and without equation number.
\starttext
\input tufte
\placeformula\startformula a^2 + b^2 = c^2 \stopformula     % no extra white
\input tufte
\placeformula[-]\startformula a^2 + b^2 = c^2 \stopformula  % extra white
\input tufte
\stoptext