Key signature and key cancellation need to be aligned

[David Sumbler]

I use Staff.printKeyCancellation = ##f in my score.

At one point the key changes from C major (concert) to C minor.  As the
piece is for a standard saxophone quartet, this means that 2 of the
instruments change from D major (notated) to D minor, and the other 2
change from A major to A minor.

A minor, of course, is the "open" key with no sharps or flats, and,
notwithstanding the negation of printKeyCancellation, Lilypond correctly
prints a key cancellation at this point on the 2 staves that require it.

The other 2 parts, in which the key changes from 2 sharps to 1 flat,
correctly do not get a key cancellation.

So far, so good.

The problem is that the actual key signatures on the 2 staves that have
them are not vertically aligned with the key cancellations on the other
2 staves.  Instead, they are printed after the key cancellations.  In
other words, each of the 2 key signatures is printed as if there were an
invisible key cancellation preceding it on the stave.  This looks wrong,
and I should like them to appear above and below the actual key
cancellations on the other 2 staves.

I have experimented with changing KeySignature.X-offset (which had no
effect) and KeySignature.extra-offset.  The latter works, but
unfortunately the position of the time signature and music which follow
remain unchanged, so that there is now an unnecessary gap after the key
signatures/cancellations.

How can I get the effect I want, and get Lilypond to take account of the
change in the position of the key signatures?

David