Fedex- how do you set shipping weights?

I have been using the Fedex shipping module. The way we were adding weights for our items was by creating a size attribute and then setting a weight to it. However, we just adding some new products that have different weights that vary from .4lbs to 4lbs and in testing that out it created no difference in the shipping cost?

I set my tare to weight at 10:1 and I even lessoned the Fedex surcharge to see if that would change the shipping and it did nothing. What is the correct way to set different weights to products so the shipping cost corresponds?

THANKS!!

Also, I've tried to play around with a product that is very light (0.1lbs) and fedex is charging $10.22??? I tried lowering the surcharge to $1.00 and nothing changed in the price, I've tried changing the tare ratio, going from 10:1 to 2:1 only took of 21 cents?? What am I doing wrong?