USPS domestic envelope option?

Normally, I ship my product in a USPS "First-Class Mail® Large Envelope." The item is just under 6 oz. and the postage is $1.65.

The USPS module calculates $1.98, which is the rate for "First-Class Mail® Package."

I'd like to keep the shipping as low as possible, so is there any way I can tell the USPS module to use Envelopes instead of Packages to calculate the shipping on certain items?

Thank you.

I am also curious as to how to change this. The products I ship should use large envelope rate, and not package rate. As the USPS shipping module stands now, it seems to over-calculate the shipping cost because it is using the package rate. Is there any way to change this?