I've noticed endurance is percentage based. As I've gotten increased endurance from the Atlas medallion, and epic power pool, when I looked at my stats, I saw that my powers were consuming more end/second than they should because of it being based off percentage rather than a straight total. So, my powers are costing me about .17 end per second more than they should be.
Granted, I gain more end/second back in regeneration, but the current system feels more like a punishment for gaining more total endurance. It makes sense to gain more end/sec back if you have a higher total endurance pool, but a higher cost for your toggles, not really. They should be a static cost, not percentage based. .17 end/second may not sound like much, but that's almost a whole other toggle worth of end being drained simply because of a higher total endurance.