It's my understanding that the EPA sucks the current off the power and PI valves, hence why you get less overdrive.
I find it to be a no issue as long as you don't put the EPA below 12-1 o clock.
Lower than that and you will want to make up for the lost territory with a good (clean) booster.
And there's of course the physics that tell you the tone sucks when you're not moving enough air.