You kinda answered your own question, but not quite. Why would an exercise make you feel the burn more at the insertion point if it didn't work that area of muscle more? Especially with a lighter amount of weight for the same reps?
Also, to illustrate the point that Bonez made; go to a mirror, and flex your triceps (preferably the dominant arm). Now flex it again, but slowly. If you do it right, the muscle will contract from the bottom up, not all at one time.
In the thread I posted that spurred this one, if you'll click on the link to the LiveSpill and read the comments, I posted that it seems to work the entire muscle from top to bottom. We're just more accustomed to feeling the top portion contract, so the contraction at the bottom grabs your attention. And it gets sore because it's used to being left out of the fun.
And I apologize for not giving you a more direct answer in the other thread. I thought that trying the exercise would answer your question. I was not trying to be short with you.