Is the 1st image photoshopped? Since I see double fields for discount % and how it's applied... or is the functionality extended by a custom module?
If I understand you correctly, you just want a 25% price reduction from the base price for the
customer group 25%.
The problem with your configuration is that you are mixing 2 different types of discounts/prices: 1. Customer group price and 2. Catalog Rule Price for a customer group.
Since you set the
Enable discount to subproducts = Yes it means the Catalog rule price discount will be used for simple products which are assigned to a configurable product.
But it's important to note that the discount is actually applied on the associated simple product price difference which is configured on the configurable product:
(image taken from this site: http://www.divisionlab.com/solvingmagento/magento-catalog-price-rules/)
So most probably the calculation for the simple product in your example goes like this:
0.28 * 0.75 = 0.21 --> this is the customer group price which was manually set in admin
0.21 * 0.75 = 0.16 (rounded 0.1575) --> applied discount from catalog rule price
So you just need to remove the catalog rule price rule to get the desired amount.
If I misunderstood you, please be a bit more detailed.