I'm having trouble resetting my margins in makeup pages. I want the makeup
pages to have equal topspace, bottomspace, backspace and cutspace,
regardless of the standard layout of the rest of the document.

Following Wolfgang's recommendation (
http://www.ntg.nl/pipermail/ntg-context/2014/079409.html), I tried the
following:

\setuppapersize [A4][A4]

% Standard page layout
\setuplayout    [width=middle,  backspace=1.5in, cutspace=1.5in,
                 height=middle, topspace=0.75in, bottomspace=0.75in]

% Title page layout
% \definemakeup defines a layout with the same name, which we alter.
\definemakeup[titlepage]
\setuplayout  [titlepage][width=middle, backspace=20mm, height=middle,
topspace=20mm]

\starttext

\startmakeup[titlepage][top=,]
bla
\stopmakeup

But, on my system, this puts the "bla" too far from the top of the page,
and it looks as though the topspace has not been set properly. (Backspace
seems ok), Am I doing something wrong or is there a better way to achieve
this?

Also, the manual says I can use the command \showframe to display frames to
help in debugging, but that doesn't seem to do anything for me?

Thanks in advance,

Mark