I have not dealt much with this topic, but was given an order today that had 4 parts, all in the same pricing group, and the system did not combine the quantities and adjust the costs accordingly.
First, is this something Epicor does? I have ran several searches in the Help files and didn’t see anything related to this.
Next, if it is, where is the help/information on this located?
After selecting Apply Order Based Discount from the Actions menu
Does anything show in the Pricing Group on the Line -> Detail sheet?
I did a test where I have a Pricing Group that has two Product Groups assigned, and a Value Break of 10% for $10,000
Creating an order with two line (one of ecah of the two PrdGrp’s in the price group), each for under $10,000, but combine to over $10,000, I get a discount applied to each
Apply order based discounts was the problem. Anyway, took a while but I found a few tings in the Help File I’ve been reading. Its not worded the way I would of thought it would be. and that is probably because it was designed by people much smarter than me! 
Yeah… The biggest catch is that the discount will be calculated even if the Order total drops below the Value criteria, UNLESS you re-run the Apply Order Based Discounts…
So if you enter a line for 10 of something that cost $1,000 each, and apply a discount (of 10% for orders >= $10,000), it will put a $1,000 discount in.
If you then change the qty to 9 (for a pr-discount total of $9,000), it will still apply the 10%, and give you a $900 discount.
You should re-run the “Apply Order Based Discounts” prior to printing.
Also saw on this is if there was price lists in Customer Maint. The hierarchy will hit that first and will go off of that list. So if your price list is one price across the board, it will not matter on qty or what Price List Maint has.