Combine shipping charges for Flat Rate Envelope when it is not an option on the item

[chrid_3386]

A user purchased a quantity of 3 from an item with a weight entered as 6 oz.  The item allows for USPS First Class and USPS Priority Mail services.   My combined shipping rules are set to combine by weight, which in this case would be 18 oz, more than USPS First Class allows.  I would expected that combined shipping would automatically select USPS Priority Mail for this order.

However, the user is still presented with the USPS First Class option:

(image is from a different account than the actual buyer so the pricing is different than the next image)

When I go to purchase the shipping label eBay has only charged the customer for a USPS Priority Mail Flat Rate Envelope, which was not one of my allowed options and the items will not fit in the envelope:

USPS Priority Mail, which was the second option available for the item and how the item will ship due to size and weight, is considerably higher cost than what eBay charged the customer for the Flat Rate Envelope:

Is there some way to set up combined shipping so that it will only choose from the shipping options I have specified on the item?  Or since I included "USPS Priority Mail" as an option is eBay allowed to choose any form of "Priority Mail" it wants (in this case the Flat Rate Envelope)?

Thanks!

[nobody*s_perfect]

Go back and see what the buyer actually paid.  Just because flat rate envelope shows up first in your label options doesn't necessarily mean that's what the buyer paid for, it's just first on the list of Priority options you could possibly ship through.

[chrid_3386]

Thanks @nobody*s_perfect, I went back and checked the actual shipping paid and it leads to more confusion and questions 😀

From the purchase label page for the order I can see the following:

Looking at all the available options this does not match any of them (again eBay allowed the buyer to select USPS First Class even though it is not valid for the combined order).

It is slightly higher than the Flat Rate Envelope cost, which is good for me, but still not up to the actual Priority Mail price.

Mostly, I 'm not as concerned about the price difference on this one order, but just trying to better understand how eBay calculates these values to try to avoid issues in the future.

[nobody*s_perfect]

Looks like there's a handling fee in there?

[albertabrightalberta]

I think if there's an error, it's on you since you're the one who set up the listing.

Will the 3 sets fit into a FRE or SFRB? 

Depending on where the buyer is located, it might even be cheaper to ship by weight but non-flat rate. 

[chrid_3386]

@albertabrightalberta, if it is on me, then that is exactly what I am trying to figure out, how to set up my listings and combined shipping properly.

Unfortunately the 3 sets do not fit into a FRE or SFRB.  The combine shipping policy I have set up is set up to combine by weight, so I would expect that eBay would not present the buyer with the option for USPS First Class, since it does not meet the requirements.  I would also expect eBay to choose one of the appropriate options defined in the listing, in this case USPS Priority Mail. 

Currently the only options set on the listing are:

@nobody*s_perfect there is a $0.15 handling fee added, but even with that the calculated cost does not match any of the provided options.