Adjusting The Weed Box Size

[tony@highcalibercustomcoat 0]

Hey There, I am having trouble figuring out how to adjust the size of the weed box. Let's say I have an image that is 2" square when I hit the "add weed box" tab it makes the box about 2.5/2.75" 

How do I make the weed box small so that it is closer to the size of the image and I don't waste as much material?

Thanks for your help!!! 

[haumana 1,220]

personally, i usually just make my own weed boxes, because I like to be able to draw in the relief lines where they make sense on how I weed things.