So there was a slight dip around 300Hz.

In box measurements after port tubes and stuffing and xovers resulted in slightly different results in this region. These were not measured at 2.83 volts, just started at 80dB/100Hz.
100 80dB 82dB
200 81dB 79dB
300 80dB 82dB
400 79dB 78dB
500 81dB 82dB

These were done at about 2 meters, mike in line between the "ears" and center of the baffle. Match between left and right would be hard to improve, this was measured "as listened to" in the room.
The last jbl info posted, detailing the 3677 system, calls the 2035 a 99dB driver. BTW, they use a 3rd order filter at 1.2kHz. with this woofer. I believe the SINGLE 2035 has close to, or slightly MORE output across the board than a PAIR of 2226J's(97dB per jbl).

Am I correct you are using the 2035's from 250Hz. AND DOWN. Below 80 Hz. they soon start their slow rolloff at the bottom. Raw data showed F10 at 60 or 70 Hz? Another issue you may want to consider, the z plot shows this driver is only 6 ohms at 200 Hz. By 100Hz, near 10 ohms. Peak at Fh(80Hz.) was 20.5ohms. Z at Fb was 6.3ohms around 48Hz. Not sure how that might be affecting your xover.

Like Wayne advised, in room measurements need to be taken with a grain of salt. You said they sound good, and that is the most important thing. Mine, in spite of the low end measurements, produce EXCESSIVE bass when I switch in EQ of +6dB@50Hz. Also, all measurements "in room" have my enclosures front baffle 3 feet in front of the rear wall...I am getting much less bass reinforcement from the walls.
That reminds me, the distance away from the wall I just mentioned can create a DIP in response when it is 1/2 wavelength, I'll try to find the reference url and post it later. Sam

in case anyone missed it, JBL has more tech data posted online at
www.jblproservice.com/support_info.htm

word of CAUTION, I saw the same xover schematic used in different systems whose HF drivers were different Z's, so verify component values to determine "if they make sense" before implementing the diagrams with "blind faith".