Value Field not adding to price

Hi, I love this plugin but have a few questions.

First question is, I have to add a fee to certain products and I used the Hidden field and put a value of 0.05 to add five cents. It shows up on the final checkout page but doesn’t get added to the amount at all. Is there a way to add a price addition to it? If so is there a way to tax exempt it (if it’s not already)?

And for my second question, is there a way to select variable products as a type? I know you can select it as an option, but I mean more like being able to select the actual variables as a type as each one requires a different additional price to be added on.

Anyways thanks for this wonderful plugin and keep up the great work.

https://www.ads-software.com/plugins/wc-fields-factory/