Multiple ossia problems

[caagr98]

The first ossia is extended too far to the left (due to system start).
The second is extended too far to the right (due to grace notes).
The third is cut of at the left (also due to grace notes).
The fourth has an end-barline, which I'd prefer if it didn't.

All of them are also unnecessarily placed below each other, despite 
there being plenty of space above.

Is there some way to work around these issues?

```
\version "2.18.2"

ossia = \with {
        \remove "Time_signature_engraver"
        \remove "Clef_engraver"
        fontSize = #-3
        \override StaffSymbol.staff-space = #(magstep -3)
        \override StaffSymbol.thickness = #(magstep -3)
}

<<
        \new Staff {
                a4 a a a|
                R1|
                a4 a a a \grace {a a}|
                r1|
                \grace {a4 a} a a a a|
                R1|
                a4 a a a
                \bar "|."
        }
        \new Devnull {
                \new Staff \with \ossia { a4 a a a }
                R1|
                \new Staff \with \ossia { a4 a a a }
                R1|
                \new Staff \with \ossia { a4 a a a }
                R1|
                \new Staff \with \ossia { a4 a a a }
        }
>>
```