nested tuplet bracket problem

[libero . mureddu3]

Hi all,
I've searched the list with no result: I have this two nested tuplets,

fagotto = \relative c, {\clef bass fis16\mf-. r16 r8 r1
                        \times 2/3 {r4 \times 2/3 {fis16 f bes}} b16-.
}
Of course, I have to move the first bracket. I tried putting \once \override
TupletBracket #'padding = #3. In the regression test, there is an example
of nested tuplets, that I tried to use without any success.
Can someone help me to solve this problem?

Hope it is  my mistake, but  this regression-test example, seems to me 
incomplete
or unclear: I think it doesn't show the bigger tuplet "6:4", that is in the
snippet , and it is not clear to me if the quintuplet is referred to a quarter
triplet (in this case, it will be better to use an eight quintuplet over
two quarters), or is part of the remaining 4 note of the initial sextuplet
(in this case it should be 5:4.

If I'm wrong, please help me to understand this "ferneyhoughian" example!

Thanks

Libero