Far as I know, there are three vessels that could be blocked during partial hanging: the carotid artery, the jugular vein, and the windpipe. The windpipe is the most uncomfortable, blacks you from breathing, etc. The jugular vein is the one that you're probably hitting; it drains blood from the head, and when you block it, all the blood in the head will swell up. The carotid artery is the one you're shooting for, it just blocks blood from going to the head in the first place. From my attempts I recommend placing pillows, towels, or something soft on either side of the rope; that way, it squeezes both sides of the neck instead of in front, which will help get to the carotid artery. Hope this helps.