slant of tremolo-beams - again

[andersvi]

LilyPond v. 2.11.57

I see there's an old thread (mar. 06) about slanting tremolo-beams on
stems of beamed notes.

How to tweak Lilyponds default way of slanting the tremolos?

I tried

  \override StemTremolo #'beam-slope = #0.3

as suggested in the thread, but it only returns a warning and does'nt do
anything.

In the mentioned thread Kurt Stone's guidance about tremolo-beams are
questioned, and 'real-world' examples are sought.  2 examples from
scores published by Edition Peters (Brian Ferneyhough and James Dillon)
follow in separate emails.

-anders