Fontconfig - Nov 2005 - Can one specify character width more precisely than with aspect?

Hello,

When searching for a pattern including character width and height:

URxvt.font:xft:Bitstream Vera Sans Mono:style=Roman:pixelsize=26:aspect=0.8

I am unable to specify an aspect ratio with greater than 1/10
precision, (aspect=0.767 is rounded to 0.7, and aspect=0.768 is
rounded to 0.8, for instance.) Is there a way to more precisely
specify character width?