It only works on a small subset of the population actually IME. That's partly due to the direction that the vertebra wants to go in towards the normal position ie the vertebra is anterior to the normal position and wants to be adjusted posteriorly, so you 'pull it backwards' with the technique you describe. So if the patient doesn't have an anterior subluxation, there's no requirement for this technique.
However the second main factor to whether you can perform this technique relates to the amount of subQ fat in the area. Too much or the wrong quality (ever notice how some fat allows you to grab the area, whilst other fat resists grabbing and kind of squidges away from your grip?) of fat prevents you getting a firm, non-painful grip on the area.
There, you can go and impress the woman with your in depth knowledge, ha.