Positioning of tremolo marks

[liang seng]

Hi, I'm using the Win98 version of Lilypond 2.7.27. I have some questions 
regarding the tweaking of tremolo marks.
1. How do I move the vertical position of the tremolo mark? Specifically, I 
would like to move the mark a little closer to the beam. I think it is 
controlled by StemTremolo and the property is Y-extent. I just don't know 
how to input the syntax. An example of the work is like this:
\version "2.7.27"
\relative
{  c8:16 c: c: c: }
2. Is it possible to make the tremolo marks slanted, as in the example in 
the manual?
Thank you.