Yes, as long as your body would stay slumped into that position when you went unconciousness. You are seeking to compress the jugular vein and/or carotid artery in the front of your neck, so it doesn't matter if there is space at the back, as long as the noose keeps pressing against your veins. If you're not familiar with the placement of the jugular/carotid, definitely Google them. You can put your fingers on them and feel them. Constricting either one will work, but I've gathered that the carotid is more effective (causes one to pass out more quickly? I'm not sure). It's on the right; the jugular is on the left.
I think I'd lean forward, cutting off both, but with more pressure on the right side (carotid). You're not seeking to cut off your breathing, so don't worry about that. You should be able to breathe normally.