All that's required is the depth necessry to receive the bar according to how high you've been able to lift it. You'll never receive in the absolute rock bottom--but it may be close and you'll sink down to rock bottom while absorbing and stabilizing the load. In either case, if it's not a power snatch, get used to squatting to full depth regardless of where you receive the bar initially. As the weight increases, you won't be able to arrest the descent anywhere else anyway.
Watch these snatches to see what I mean: