500mg test with no AI is around 100 E2, with a full dose of 3rd gen AI, it is about 50. On 1g test, with no AI is about 200, with a full daily dose, it's about 100. Acceptable level of E2 is relative to how easily you get sides, but I would always use at least a tinny AI dose if you are on "a lot" of test (a lot is subjective, personally I consider that .5-1g).
Any chance we can get a pic of your bloodwork with exacvtly how much test you were on? The only way you could have your E2 that low on a decent amount of test is it had to be very underdosed.
400+ would take 2g+ test with no AI, otherwise I would suspect something else you are taking is messing with the test, this is especially possible if ELISA methodology is used. E2 and testosterone compete with each other, so a lot of test with very little E2 (even if it's in normal range) would cause lots of low estrogen sides. BESIDES this fact, you CANNOT get it into normal range, no matter what you do, because you can only lower E2 by 50-60% with an AI (in males, completely different in postmenopausal females).
Not possible, your test was way, way, underdosed.
http://www.professionalmuscle.com/forums/beginners-forum/65807-estradiol-1g-test.html