How can I set up tiered volume discounts without enacting a waterfall effect of multiple discounts being applied?
Currently at Craft Commerce 1.1 this is not possible with the current discount engine.

We would need to implement features like a min qty AND a max qty for the discount rules. It is on our radar.

Fee free to vote for extended discount conditions features here: http://feedback.craftcms.com/forums/295386-commerce/filters/top