A is the pivot point... usually a single stripe.

Not sure on the other stuff as I was under the impression that abcd/abcd/abcd was Asymmetrical (Maple Leaf, Buchanan, Stewart Hunting to name a few) and abcdefedcbabcdef was symmetrical.

There are 'ABAC' tartans like black watch where certain elements get repeated MORE than once in a sett (the green with the black line running down the center). Is that what screwed you up?