Are there no mathematicians in the zone that could give a definitive answer to the ratio of sizes for say three different ones that would give the best space filling ?
I can do it in 2d but not 3d, simply by using coreldraw and playing with circles !

Edit
In case anyone asks, it's 1 x 10mm circle to 1x 1.5mm circle to 3 x 0.6mm circles.

Edit 2
I've just googled "spherical packing mixtures".
I think the word "mathematicians" should be changed to "mathematical genius" in the first line. (chair)

John