Positioning text below notes at the same height

[address@hidden]

I have made a small function that allows me to put out the fret number 
(of a guitar) below a note. My problem is that the text is positioned 
below the note at a specific distance. Which means that if the note is 
high on the staff the text will be high and if the note is low on the 
staff it will be lower.

Is there someway of setting that I want all text the same distance from 
the staff, not from the note?
// Anders
PS! This is the first function I have written so please suggest 
improvements!!

\version "2.14.2"

\header {

title = "Test of Fret numbering"

subtitle = "E9th Pedal Steel Guitar"

arranger = "Anders Eriksson"

}

%% -------------------------------------------------

%% fret-number.lyi

%% Function for creating a fretnumber below note or chord.

%% Call:

%% c4-\fN "8"

%% <c e g>-\fN "3"

%% -------------------------------------------------

fN =

#(define-music-function (parser location fretp) (string?)

(make-music

'TextScriptEvent

'direction

-1

'text

(markup #:line (#:box (#:italic fretp )))))

%% end of function fN

\relative c' {

c4-\fN "8" d e c'-\fN "10"

}


--
English isn't my first language.
So any error or strangeness is due to the translation.
Please correct my English so that I may become better.