gloo, from one beginner to another, I always rack from the primary (well, I don't really rack, I just pour it thru a strainer) around 1.015 to 1.010. From what I gather this is the safest way, I'm still going to be fermiting when it gets in the secondary so I will purge any air out with CO2, and I figure head space isn't that important. It is important thou when you don't have fermentation going on because you have no way of purging the O2 out. That's when you need marbles or top it off with a like wine. I haven't had any problems doing it that in all my time making wine (a full 6 months). Would someone please correct me if you see a problem with the way I'm doing it.
Thanks
Semper Fi