Modify formula for bouncing object to increase restitution

Question

I originally started a thread over on Stack Overflow about this but it's diverged into mathematics which is way beyond my understanding.

Basically I have the following formula (it's JavaScript but I don't think it should really matter) that represents a bouncing object, with gravity:

Rubber: function ( p ) {
    var pow2,
        bounce = 4;

    while ( p < ( ( pow2 = Math.pow( 2, --bounce ) ) - 1 ) / 11 ) {}
    return 1 / Math.pow( 4, 3 - bounce ) - 7.5625 * Math.pow( ( pow2 * 3 - 2 ) / 22 - p, 2 );
}

It works nicely but I need to increase the 'bounciness' of the object. I believe this is called 'restitution'.

I've played around with the numbers but it's admittedly just trial and error (mostly error!) and just can't get it to work as desired. I wondered if someone here who understands this kind of thing could say whether it's actually possible to increase the restitution of the object within the bounds of this equation, or if not, how it could be modified such.

Many thanks folks - I really appreciate it!