Seems you hit the nail on the head Steve. I ship most small orders in padded envelopes.
According to the postal worker I spoke to, if you select the "large envelope option" (less than 3/4" in thickness) shipping cost will be less. But, apparently, the size packages I've been shipping are more in the "parcel/package" category. Therefore, I will be selecting the package/parcel option from now on. It looks like it will only average about $1 or so more per package.
I'm guessing that many local post offices must let this error slide a lot because I've been doing it this way for a couple seasons now without any word back from recipients.
But I'd rather pay the correct shipping up front so no problems come up down the road. I sure wouldn't someone to miss out on their package because I made a mistake with postage :-/.
If it looks like I'm beginning to lose too much $ in shipping, I may have to bump my minimum shipping charges to $4 instead of just $3. Not too big of a deal I think.......