The local postoffice was also overcharging me for packages. What everyone who has this problem needs to do is to go to their web site, under postage rates go to the large envelope box and click on the question mark. This takes you to a description of the large envelope which includes the statement that if ANY of the 3 dimensions are exceeded then it is a large envelope. This is important when they try to charge you for the parcel rate for a large envelope. That frequently happens when the thickness is between 1/4 and 3/4 inch. Here is the link:

http://postcalc.usps.gov/PopUps/pop_up14.htm

If we can get enough people to complain then they will eventually change the rates so the Postal critters will understand what the correct charges should be.