AbleCommerce Shopping Cart Software

Good afternoon. I am using version 7.0.3 build 12458 and have a question about how volume discounts are applied.

I have a category of products (socks) and I'm trying to discount them as follows:
Quantity
from 1 to 1 - $1.00
from 2 to 2 - $3.48
from 3 to 4 - $4.30

I have all the socks in the category added to the discount, and in Configure / Store I have it set to:
Discount Mode: Group By Category

When I add multiple sizes of one discounted sock to the cart, the discount is applied correctly.

However, when I add different products (e.g. tube sock, calf sock, and crew sock) that are all in the same category and all have the volume discount applied, each one gets the "1" quantity discount ($1) rather than the "3-4" quantity discount of $4.30.

Am I misunderstanding the difference between Line Item and Group by Category mode?

Any suggestions would be greatly appreciated.

Thanks!

It appears I have answered my own question.

If you add a complete category in its entirety it works as expected - discounts are applied across products. If you add products within a category individually it does not work.

Said differently, you are unable to use this kind of volume discount if you want to exclude any products in a category, you must discount them all.

I hope that helps someone else.