There are 3 great and easy ways of reducing your dimensional weight.
You can use any of them to reduce your weight.
Using all of them is best.
Make sure your box is as compact as it can be. The smaller the box the less your dim weight will be.
THE SCIENTIFIC OPTION
REALIZE that the more you reduce the shortest side of your box, the more it will cut your dim weight. (Trust us.)
THE SMART OPTION
Get a "custom dimensional divisor." See here for more info on that.