TimeSignature as fraction: gap between numerator and denominator

[Werner]

Hello, 

I used 4/4 instead of C via
\override Staff.TimeSignature #'style = #'()
but the cyphers were huge.
So I added
\override Staff.TimeSignature #'font-size = #-2
But while the cyphers now are smaller, the numerator-4 stands still very close
on the top of the denominator-4 without any gap, both together in the (vertical)
middle of the stave.
I would prefer both ciphers (vertically) centered in the upper and lower half of
the stave respectively (means the numerator between the third and fifth line of
the stave, the denominator between the first and third line) by default.

Is there any solution?

Greetings

Werner