Need help with CD (JBL 2405H)

So I recently purchased a pair for some JBL L300 clones and unfortunately have to replace the diaphragms in both. I ordered some 16ohm replacements from speaker repair and one plays loud crisp and clear but the other one sounded subtly quiet. I disassembled the quiet one and believe the problem was solved by realigning the voice coil and phase plug. They both seem to play with the correct spl now.

I decided to hook them up to DATS V2 to see the parameters of both and compare. One has an fs of 460hz and the other has an fs of 820hz. How can their fs frequency be so low and why so different? They both sound good but I was imaging they would have an fs around 4 or 5khz. I would figure a lower fs is good, no twist on the diaphragm creating less stiffness. Also, both impedance plots look very similar.

Question 1: do CD's and horns create Wierd measurements using test systems like DATS?

Question 2: how can I be certain that the diaphragms are correctly aligned?