How to control the speed of "Scale" change?

[d4rk3lf]

Well, it seems that balls completely disappear when scale is around 60-65%. 
I am not sure why this is going on (maybe because of interpolation parameter) 

So I animated to 60%, and extend scale animation to make it as close to 130-190. 
You can tweak it further now, and get more precise... I just quickly did this.