ECM added with shipedit can not exceed 6, it is a hidden shift that is not displayed, the game does not support above 6.. ECM added using your ECM console is in addition to the "natural" ECM shift applied by the shiplist.. much like looking at the Rom Cloak.. the cloak adds ECM to the cloaked vessel, however, the shift is not listed on the screen... 6 ECCM usally balances the shift out, however this still will not outweigh the ECM from their console that the cloaked ship applies.. same goes for other ships.. natural ECM will apply, but will not be seen... ECM from the console will stack on top of the natural ECM... WW shuttles also give an ECM shift as well...
hope that this info helps.