Softimage Xsi: particle size

I wanna animate the size of the particles where I put an instance geometry. The problem is that once I have chosen my instance group I have no more control on the size in the particle overview control. Changing the size don't change anything. And if I animate the size of the instance group it affects the particle systeme but not in an absolute time not in an age percentage...

IS there a way to resolve this problem ???


I got another question totally different. I wana create to position animation curve and then mix her. eg : a animation for the big movement and on for a little shake. How can I do that ???