I don't think it matters in your case as you had a clean emg and if you have ALS type fascis they are picked up by the test.
As for location, my partner's pre- diagnosis emg revealed them in all limbs, including clinically unaffected ones, as well as in his atrophied left hand/arm. A year on he still has fasciculations all over, although legs still strong.
As a side note, I was having a heated debate about something yesterday, and noticed my right arm twitching violently. It made me smile, in an ironic kind of way as there is no way that we are both going to end up wit ALS (although I have heard of one such case...)