If you look at the hanging megathread, I'm sure you'll find examples of people who said they would attempt partial and then did not return to the site.
There's no need to limit yourself to these forums though - go on any gore site and search 'suicide', and you'll find countless examples of people who were found hanging with their feet in contact with the ground. The empirical evidence points towards the reliability of partial as well: The work of Geo Stone, which can be found in the
Resources thread, reported that people who CTB by hanging are more likely to be found with their feet in contact with the ground than in the air. This doesn't necessarily mean that partial is more effective than full suspenion, as we don't know the rate at which each version is attempted - it could be that very few people attempt full suspension, so that the number of successful CTBs per full suspension hanging attempt is actually higher.
The users who initially advocated for partial claimed that it is completely painless and rapidly causes unconsciousness, but many users who attempted disputed this. Some people struggle to locate the carotid arteries, and end up restricting the jugular veins, which causes the sensation of one's head 'exploding'. There is information in the megathread about where to place the knot to best apply pressure, but it's going to vary depending on the individual, so you'll have to experiment. I will say, however, that in many of the compilations of CTB by hanging that I have seen on sites like the YNC, the knot was placed
Theoretically, there's nothing wrong with this method; if you restrict the carotid arteries with sufficient force, you will lose consciousness rapidly, just as someone placed in a rear-naked choke-hold would. You can simulate this sensation by taking a rope or some other ligature and pulling it closed around your upper neck, without tying a knot; you'll feel a sort of 'buzzing' sensation, and your hearing and vision will start to dim. You won't actually be able to pass out, but you'll have an idea of what you might experience before passing out.
Finally, I advise you to use the search function to find examples of people failing this method - it could be that there is some way to fuck up this method and permanently injure yourself that I haven't considered, and like any other method, it's useful to look for evidence
against its efficacy, in the way that a scientist attempts to disprove a hypothesis. This way you can ensure that you don't get hurt, or fuck up too badly.