Help with formula for variable length rectangle

Hi All,
This might seem like a simple request, but I'm banging my head on the wall so I thought I'd ask for help.

I want to creat a rectangle in report designer that changes length with data input, so I wrote this formula = ([ordered_gross_2013]/100) * (525/100)) in the max-width area of the style section, just like the Inventory List report example in the welcome area of report designer, but for some reason the rectangle width doesn't change. I'm sure it's something simple I'm overlooking but any help would be appreciated.

Thanks.