Resizing stack

[Jim Hurley]

I don't think I understand the new resizing utility in 2.1

I have a rectangle graphic, centered on the screen.

I would like to resize it as the stack is resized so that halving the 
width of the screen haves the width of the rectangle. It should also 
keep the rectangle centered on the screen.

In 1.1.1 I can do this by Maintaining dimension relative to the right 
and left side of the screen.

But I can't find any  combination of Solid or Wavy bars in the "Scale 
selected object" window which accomplishes this same feat. Shouldn't 
one be able to select a Wavy bar (proportional scaling) relative to 
the *left* side of the stack as well as the right side?

Jim