finger/ note position

[pabuhr]

The following snippet illustrates two problem I'm struggling with.

1. In the first bar, the finger number "2" is not beside the B note because of
   the sharp above it in a different voice. I can tweak the finger number back
   into position beside the B note, but I have a number of these cases in the
   piece I'm working on so is there a global way to prevent this interaction
   between accidents and finger numbers in parallel voices?

2. In the second bar, the A note stem is clashing slightly with the D note
   above it. I've tried to push the A note to the right using \shiftOnnn, but
   I've run out of "n"s. ;-) How can I push the A note further to the right to
   avoid the stem clash?

\version "2.16.0"
\language english
#(set-global-staff-size 30)

su = \stemUp
sd = \stemDown
fl = \set fingeringOrientations = #'(left)

melody = \relative c'' {
        << { \sd \fl c,4 <b-2> } \\ { \su \fl g'8\rest g8 gs4 } \\ { \su \fl 
e'4. d8 ~ } >> |
        << { \sd \fl a,4 d } \\ { \su \fl \shiftOnnn a'4. } \\ { \su \fl 
\shiftOff d8 c4 <c fs>8 } >> |
}
\score {
        <<
                \context Voice {
                        \key c \major \time 2/4
                        \melody
                }
        >>
} % score

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