Beamed rests

[Fulvio Turra]

Hello all. I am a new Lilypond user and I'm in trouble trying to reproduce a beam over a 16th rest, between two 16th notes, as in the followin picture:

The only acceptable solution I've found so far is to apply \set stemLeftBeamCount = #1 to the rest, but the result is this:

Here's the simple code:

a'16[ \set stemLeftBeamCount = #1 r a]

It's close but it's not perfect: the rest is halfaway outside the staff and the second 16th beam is too long.

Anybody has any suggestion on how to improve this output?

Thanks in advance

Fulvio