There are many threads on this at the Reference 3a Cirle on audio circle. The cirlce is realitivily new, if you go back a few pages you wil find a bunch.
Take a look, they are very helpful:
http://www.audiocircle.com/circles/viewforum.php?f=53
I will also save you a bit of reading by giving you a run down, but there is still other information worth reading. Basically they say if the middle or the top 1/3 of the woofer is on axis with your ear that is best. It is not like other speakers were you put the tweater on axis, on 3a's it can be a little bright sounding if you do that. I would listen to yorus and start to lower or raise your self accordinly until it works best for you.
Cheers,
Nick