It's a great idea in principle ie: 2 x identical items one has free post $10, the other is $2 with $12 postage, hard for shoppers to work out. Anything that makes things harder is bad for everyone.

But I can see the point about bulk lots in more expensive postage boxes and even larger heavier items that will incur the extra fee on something ebay shouldn't be charging a fee upon (post) in the first place.

Sometimes a one size fits all doesn't always work.

Obviously if your post is $30 the ebay 10% costs you another $3 so you have to charge $3.34 because when you put the $3 extra on to cover the 10% ebay fee,  that $3 is then slugged with .30c, you put the $3.30 on and you're slugged $3.33 etc, etc...