I used Safale S-04 and had less than 2 inches of head space. 2.75 gallons apple juice in a 3 gallon BB. It was fine. Never a problem.
Primary: 3 gallon cider S-04
Secondary: Valentine Apfelwein Clone 1 Gal
Bottled: Halloween Apfelwein Clone 1 Gal
On Deck: 90 Shilling Clone