Here's a good way to make sure your bumpers are put together well. If they aren't, all of the extra space that comes from the bumpers will add to your total size. There's lots of talk about how to get the most out of your total robot size limit.
http://www.robopromo.com/category_s/1826.htm. One thing that teams are considering doing is just corner bumpers of 6 inches to save on weight when trying to scale the rope
http://www.robopromo.com/product_p/rp-2018.htm