It's unlikely that you are a poor responder to aromasin. I'd be willing to bet you aren't absorbing it properly.
Here's something most people don't know-
You must take your aromasin with a fat source (preferably a meal containing a decent amount of fat), and dose it twice a day for it to be completely effective.
My suggestion is take a shot glass of olive oil or MCT oil with your aromasin. I prefer the MCT since it has little to no taste and is very light- and the body is unlikely to store it as bodyfat. MCT oil can be found at places like swanson vitamins, vitahealth, and a lot of online supplement companies. Usually like $15-20/liter.