I was going to answer the small enclosure/large enclosure question, but Pythoninfinite and cris said pretty much what I was going to say. The quick answer is that it's easy to control everything (heat, humidity, escape options) in a small enclosure. As has already been mentioned, baby lace monitors are incredibly shy and don't like to be out in the open, because in the wild they'd be food for everything. Having everything they need, such as basking spot, hide spots, water and food, close at hand is important. They'll always rank security higher than everything else, so as cris said in a large enclosure they may just hide in a corner and not emerge.