When the moon moves completely into the Earth's dark shadow cone (called the "umbra") we call that a total lunar eclipse.  At the moon's average distance from Earth of 239,000 miles [383,000 km], the umbra measures roughly 5,800 miles [9,334 km] in diameter. The moon is about 2,200 miles [3,540 km] in diameter. So there's no problem in getting the moon completely immersed in the umbra; there's plenty of room.