The order the two shards were put into the altar when combining them into a single shard was tested. It was previously suspected as you suggest that the first shard placed into the altar was the one that imparted the "dominate" focus. This was later dismissed when someone made a dual shard that ended up having the focus of the shard that was put in second as the "dominate" focus of the dual imbued shard.
What we have thus far seen to be true and yet to be disproven is that in the description of an apsect/balance, the focus listed first ends up being the "dominate focus".