Dear list,

My adventures into the world of grids continue. In the linked file (slide_grid_overlay.pdf) there are two things I cannot yet achieve:

    1. I want the baseline grid to evenly (vertically) divide the text area, but my code produces a smaller height of the first line and an additional space at the bottom.
    2. The number of columns is 21.5, that is the first column is 0.5 units wide and the rest are 1 unit wide.
   
How would I achieve this?
Here is what I got right now:

\definemeasure[xheight][0.1in]
\definemeasure[base][3\measured{xheight}]

\definepapersize[slide][width=80\measured{xheight},height=60\measured{xheight}]
\setuppapersize[slide]

\setupinterlinespace[line=\measure{base},top=1]

\setuplayout[
leftedge=\zeropoint,
rightedge=\measure{zero},
leftedgedistance=\zeropoint,
rightedgedistance=\zeropoint,
leftmargin=\zeropoint,
rightmargin=\zeropoint,
leftmargindistance=\zeropoint,
rightmargindistance=\zeropoint,
width=middle,
cutspace=2\measured{base},
backspace=2\measured{base},
topspace=2\measured{base},
header=\zeropoint,
height=middle,
bottomspace=2\measured{base},
footer=\zeropoint,
grid=yes,
columndistance=1pt,
columns=21.5]


\showframe
\showgrid

\starttext
\input tufte
\stoptext

Link to file: https://drive.google.com/drive/folders/1KpYbDlukvSCirKkFvJICOX3wABl_83bW?usp=sharing

Sincerely,
Stefan