particular: linking to a nested 3D null object

hi all

I've got an instance of particular that I'd like to parent to a nested 3D null object.

It's working properly with one null; but when I parent that null to a second null, in order to get some secondary animation, particular doesn't follow the position anymore

is there a way to get it to work, when using a nested null system? 

thanks!

ML

ps I'm using the pickwip method to link position for x & y, and then pickwip separately for the z position