Offsetting time and position of several layers relative to preceding layer

Question

Hello -
Pardon the newbie questions, but I've keyframed 'Black Solid' moving along the x axis and basically would like to duplicate the layer (perhaps with a new color) several times so that each 'new layer' follows the previous layer and offsets itself a certain amount of pixels...say 20px for example.
I found a simple expression that I applied to the first dup'd layer and it works fine but I can't figure out where to tell it to offset 20px to the left of the main layer.
thisComp.layer("Black Solid 1").transform.position.valueAtTime(time -.1);
I suppose I'm trying for a cascading effect + offset.
Thanks!
gj

Answer 1

Everything is spelled correctly. Yes, the problem seems to be that I'm trying to refer to shape groups, not proper layers. This was done by importing an Illustrator file and then creating shapes from vector layer. (Each shape gets its own "group," which apparently AE doesn't see as layers.)
This is also weird, since simple expressions, such as
content("shape-1").transform.position-100
work fine. I guess that's because there's no layer reference, only a reference to the shape name, "shape-1".
Is there a way for an expression to address position and time for these "non-layer" shapes?
Thanks for your help.  :+)