Discount Code Applies to ALL lines, vs. the specified line in the Price Set Field

I have set up a discount to apply 100% of the price to specific Price Fields from my Price Set, however, the discount is applied to all lines. We have tried editing the Discount to a specific amount instead of a %, and the result is the same. This is a code used applicable to only 2 of the 3 price fields in the Price Set designated for this event. The Price set field I am using has one mandatory price field and an additional optional price field (there is at least one charge, with the optional second). In this case, we've chosen (in the setup) to apply the discount code to the mandatory field only, but is being applied to both.

*We have also tried changing the Discount Amount Type from a %, to a fixed amount (fixed amount reflecting the on mandatory price field), without success, as the discount 'zeroed' out all amounts.

Currently using CiviCRM v 5.58.1 and CiviDiscount v 3.8.8