Yesterday I tried to layout a bunch of program windows via xdotools moveto and resize. In theory they should have been all the same size, but they came out all different, and none had the targeted size. They all had space around them. What is involved in this process? Are there invisible borders, or stuff like that?
Autsch! I would never do that… X11 is such a broken mess, but then my window management needs seem to be very different from yours.
Applications do have a say in how big they get rendered (typically by giving a min/max/preferred size), which window managers may or may not resepct/adjust for after the window comes up. Maybe it is just that.