Bash/GolfScript, 72 bytes, score 2⁶/72 = 8/9 (~0.888...)

.~0 () 
{ 
    declare "-f" @* ".~0" " ()
 "+@n.;
    echo '.~0;'
}
.~0;

Contains a single trailing space on the first two lines.

Try it online in Bash.
Try it online in GolfScript.

Simply modification of @jimmy23013's answer for the "Write a Polyquine" challenge. The modification that was done was removing the trailing space after the third line, and changing \n"+@n.; to \n "+@n;.

Bash will print lines 1 and 2 like this:

.~0 ()    <- Trailing space
{         <- Trailing space

And GolfScript will print lines 1 and 2 like this:

.~0 ()   <- No trailing space
 {       <- Both leading and trailing space

Here the base program, Bash output, and GolfScript outputs respectively with the new-lines replaced with \n:

.~0 () \n{ \n    declare "-f" @* ".~0" " ()\n "+@n.;\n    echo '.~0;'\n}\n.~0;
.~0 () \n{ \n    declare "-f" @* ".~0" " ()\n "+@n.;\n    echo '.~0;'\n}\n.~0;
.~0 ()\n { \n    declare "-f" @* ".~0" " ()\n "+@n.;\n    echo '.~0;'\n}\n.~0;

      ^^^ Note the difference here