Oh, it's about That long....
Back when we ordered an ATN Snuffer we provided the measurement of the luff of our standard spinnaker, and I was told to err slightly on the short side.
i.e. it's normal to have a foot or three of material sticking out the bottom of the tube.
If your chute is standard, and not "over sized" I imagine that someone here knows the luff lengths...
It might even be the same for the E-39B.
Here's their page:
http://www.atninc.com/atn-spinnaker-sleeve.shtml
I see a phone # and email contact listed. You should confirm the "sleeve" total measurement info with them, too.
I should point out that's been over a decade since we bought ours, so my memory of the sizing might be hazy....
Since adding that gear, at least we do fly the spinnaker at least once or twice a season. It's a great sail, but the takedowns were a hassle.
Best,
Loren