Point 1 -
The palp of your index finger is clobbered with sensory nerve endings, the nape of your neck has very few. The point is that there areas areas of the body that generate a lot less input sensory-wise.
Point 2 -
How input from sensory nerves gets translated into something depends not so much on the input but the processing system -
A. how many input points are involved
B. how they are routed
C. how they get interpreted, ie, the brain can turn off pain input in the medulla oblongata - think aspirin or NSAIDS, or inebriation.
There is also the phenomenon of pain threshold. Some people do not feel very much pain - probably due to something in the "C" category above.
Biology is not like Math. There are no theorems, it's very messy down inside those bags of chemicals. Physical laws apply, of course, but in terms of systems analysis: cellular systems are leaky as hell, and subject to all kinds of varying responses to the exact same set of stimuli.
For example, I have virtually no sense of smell. An old man puked in a restuarant we were eating in - and everybody turned green from the smell, including the staff guy trying to clean it up. I took the mop, cleaned it up.
No problem, everyone else had cleared out of the area.
The point is my sense of smell is shut off. Inputs of all kinds - pain, heat/cold, smell, vision, can all be limited in some way. Or exaggerated.
It is not an absolute value thing.