running aromasin at 6.25 mg ED wouldn't be a bad idea.. actually it most likely is a better idea than running it at 12.5 mg every other day. I can't remember what the exact half-life is, but i believe it is around 25 hours. So there is always a chance of something converting to estrogen in between the days you use it. Armidex on the other hand has a half life of almost 3 days, so that will cover the EOD spread.
but you have to remember with a test, tren, mast, var cycle, the only hormone that will convert to estrogen is the test, and the masteron has AI properties. So 6.25 mg ED or 12.5 mg EOD would be fine. Or .5 mg of armidex EOD.