Hi Brian -

ShippingEasy offers USPS published rates, and we post these to our Support Center for easy reference.

• ShippingEasy's USPS Rate Tables

Your current plan (Starter) has access to Commercial Base Pricing (CBP). The CBP rate for Priority Mail, Medium Flat Rate boxes is currently $11.95. In contrast, the Commercial Plus Price (CPP) is $11.60. 

Since ShippingEasy does not have a rate quoting API for WooCommerce shopping carts, I can't say why you're receiving a different rate than USPS published rates through the plugin that you're using. However, it might be a worthwhile question for the plugin developers.

On a related note, if you're using USPS Priority Mail, you might consider their Regional Rate boxes as an alternative to Flat Rate boxes. Regional Rate is a unique shipping option that offers Zone dependent "flat rates". In other words, the rate is based on the package type and which zone (how far) the package is traveling to. The lower zone (shorter travel, generally), the less the postage. You can learn more about Regional Rate shipping in this guide:

• What is Priority Mail Regional Rate shipping?

The Medium Flat Rate box is between the sizes of their Regional Rate box options. You can use this guide to review the sizes:

• Package Sizes and Dimensions: USPS Domestic

For the larger of the boxes (Box B), Regional Rate is going to save you money over the Medium Flat Rate box for Zones 5 and below. Almost any destination for the smaller box (Box A) will be less than the Medium Flat Rate box. Just make sure that you otherwise meet the weight limits of Regional Rate boxes.

If you're interested in incorporating Regional Rate shipping into your options, I recommend also looking into setting up a Shipping Rule in ShippingEasy that flags orders that are better suited to Regional Rate. This is an example rule to help you get started:

• Best of Rules: Assign USPS Regional Rate Box to shipments with specific zones

Let me know in the comments below if you have any other questions. Thanks!