I always seem to have this problem..
Whenever I add a custom scale attribute to a particle it never shows up under General Options>Scale after i've made the expression, so i cannot use it. It only shows up under Object Index but it doesnt scale the particles if i use that.
Rotation works and im making the attribute using the same method, but scale doesnt work. Does anybody know i can fix this? Please let me know.
I am using Maya 2010 if that makes a difference.