By trial-and-error I’ve come up with the following. It seems like a hack but both variants are close enough to my requirements that I would be able to work with one of them.

There’s still one catch: When I change the caption key „location“ to „bottom“ together with „inbetween={\blank[-\strutdepth]}“ the picture is aligned with the black line (top of the first text line). 
This would actually be the preferred solution also for „{left,high}“. Yet I couldn’t find a possibility to shift the picture vertically by some millimeters.
Is there?


Best regards,
Florian.




\useMPlibrary        [dum]
\setuplayout         [grid=yes]
\setupinterlinespace [line=20pt]


\setupcaption [figure] [
						location={left,high}, 
%%						location={bottom}, %different alignment
						number=no,
%						inbetween={\blank[-.01mm]}, %Variant 1: picture top-aligned, caption on grid
						inbetween={\blank[-\strutdepth]}, %Variant 2: picture and caption top-aligned, caption not on grid
						]


\starttext
\showgrid

\startplacefigure
  	[location=top,none,title={There is not so much basic instruction, as of now, as there was
    in the old days, showing the differences between good and bad typographic design.},
	]
  \placeongrid[max]{
  \externalfigure [dummy] [width=.6\textwidth]
  }
\stopplacefigure

\input zapf


\stoptext







> Den 6. apr. 2017 kl. 10.12 skrev Florian Grammel <florian.grammel@gmail.com>:
> 
> At http://tex.stackexchange.com/q/362215/6819 I asked: How can I place the top line of the caption (location={left, high}) on the grid and have it align with the figure at same height.
> 
> I hoped this to be solvable by some simple instructions that I just haven’t been able to figure out. But Henri Menke suggested in a comment that the mechanism might not be implemented.
> Is this really the case?
> And if so: is there any way to achieve the alignment anyway?
> 
> I’d greatly appreciate any help as this is an important requirement for my present project!
> 
> Best regards,
> Florian.
> 

____________________________________________

Florian Grammel

Copenhagen, Denmark