Is the fixed spacer broken?
I use a separate stave for Capo chords so that they can be nicely aligned above the standard ones (mostly for real-estate reasons) with nice and easy transposition. I make that stave as small as possible (one line, no everything, and obviously hide the rests etc) so that it doesn't take up too much space, but it invariably still takes up a bit. To get around this, I've been using the fixed spacer to dictate exactly how far that stave sits above the rest of the system.
But now I can't. And I can't work out why. I managed to get a half-decent looking score by fiddling with a couple of settings and picking a very precise fixed spacer size, but if I'm outside of the range of 3.92-3.95 or exactly 4sp, it bumps back to around 9sp minimum. Unless I change them one at a time (just discovered now) in which case I can do what I want for most of the staves, but as soon as the last one of the page gets close to where I want it, the whole thing jumps back again.
I've set the minimum stave distance to 0, but that doesn't seem to make any difference at all...