[plt-scheme] draw-text and platform

I have troubles using draw-text and getting a same size display on different 
platforms; and even on different linux distributions... I made my code under 
debian/linux, it displays as same under Mac OS X and FreeBSD, but under Red 
Hat Linux 7.1, strings are displayed quite larger and that makes my interface 
become ugly and i cant do with that.

Is there a way to ensure this will display as same on every platform ?
In my code, I set font size with 
    (send dc set-font (make-object font% 16 'modern 'normal 'bold #f))

I thought size of fonts are the same every where but it doesn't seems...
Maybe is there another value to set or is it a system wide config failure ?

Thank you