I think that if you're skinny, it's easier to get in and around their bones (ribs and hips), and that may have a greater effect than having layers of fat already sitting on top of those areas. If one's skinny, their tendons/nerves may also be easier to get, possibly, as there's less ground you have to cover to find them, but, it may the same or worse for a bigger person, since there's more 'sensitive' ground to cover.
Despite some advantages/disadvantages one might have because of their weight, or lack thereof, I think it would depend on the individual's sensitivity, all-in-all. So, basically reiterating what everyone's said thus far. A larger person may have more endurance than a skin and bones person... or not, it all depends on the situation and persons involved.