I think a fuller cooker is definitely more humid, but more mass requires more fuel and also effects the air flow in the cooker and how efficiently/evenly the smoke/heat/air moves through the pit. I think....maybe.....
And probably the design of the pit has plenty to do with how it reacts to the quantity of product being cooked.....
Fletcher's Brooklyn Barbecue
The Hampton Smoker Blog: http://backyardchef.blogspot.com
7' Meadow Creek reverse flow w/ a 4' grill on the nose, named Large Marge
48" Klose Backyard Chef named Wubby
Willy the Wonder Grill
Weber Kettle named Georgiette
ECB Spider Web Collector Model
Char-Griller Smokin' Pro Firebrick Supremo