I think it is somewhere in between BPEL and NBPEL. For guys with a pretty thick but pliable fat pad, it is probably closer to BPEL than NBPEL. For very slender guys, the difference between the two may be as little as .25" and then the "insertable length" may be closer to NBPEL.
A guy over at Thunder's enlarged the hole in a compact disk so that he could put his penis through it, push it down against his pubic bone, and then measured what stuck out from the CD.
I am a little embarassed to admit that I did something nearly as ridiculous. I took an old clear plastic bottle that used to contain camp soap, and cut a circular hole in the top so that I could insert my cock and push the thing frimly down against my pubis. Since you can see through it, you can see how far out you extend.
Here is what I found: 1. A clear, hard plastic bottle is a lot less fun and less comfortable than a vagina. 2. I have a BPEL of 8", a NBPEL of 7" and an "insertable length" of 7 1/2".
I think the CD guy's results were similar. If I remember correctly, he had less fat pad and his measurement might have been a bit closer to his BPEL.