[NTG-context] space around formula

The space around formula with \placeformula is a bit too large to my taste, even in the case of \setupformulae[spaceafter=small]. Because setting this to 0pt didn't make much difference, I had to resort to spaceafter=-1ex. Why is there seemingly always such a large space around the formula? Why not a much tighter boundary? Furthermore, it seems that there is no difference like above/below-displayskip and ditto displayshortskip as in Plain TeX. At least, I could not find it. Or did I miss that? I consulted the wiki, but the information is not found. Hans van der Meer