.... but if the JBL 2226 goes down to 40Hz, and the W only goes down to 50Hz, maybe you should be taking the measurement from a slightly further point.
I don't think you're getting the full wavelength.
Also, maybe try a reading with the box up on it's end.
Plus, I'm a tad intrigued.
You mention that you're going to cross these at 50Hz from your Sub.
What are you using for a Sub?
ps: I do so hope you remembered to pull Dizzy out of the back of the box before you screwed the back panel on.