I am working on a new template for our site, and was working on configuring the One Click Upsell (https://support.americommerce.com/hc/en-us/articles/1260803222169-One-Click-Upsells). I noticed that the $$ADDITIONALADDTOCARTPRICE$$ merge code always show the additional price for only a qty of 1 for the checked items, regardless of what you put in the qty box.

Here is a screen capture: https://i.imgur.com/jgyVsgm.gif

In the screen capture you can see that no matter what number I put in the box, the price of the additional items does not change.

So if you enable the QTY boxes for that widget, that renders the "Costs of additional items" line as useless, as it is not accurate.