Mate, it's a US forum; the only falcon's these guys see are from the 60's, and Option Audio is an unknown brand. Shoulda asked on MEA!
ANYWAYS...
First thing i'll tell you, is unfortunately the OA Extreme's are NOT a good sub for playing lows. Their FS is up above 38hz, and the EBP favoured being sealed.
Having also built four "low tuned" systems for them, they just don't have the authority down low like other locally available subs: Earthquake DBXi, SoundStream SPLX, Mach5 IXL etc.
In three of the four systems, at least one sub has died.
But, if you want to still get loud & low with what you have, since the EB Falcon's have a low & flat boot, you can try sub up, port sideways. We did this in a VS Commodore with 10yr old basic RF stuff, worked out well:
(IF you can't see the image, add "Riverside Customs Miguel" on facebook.)
2.25-2.5cuft NET per sub is optimal, we tried 2.8cuft NET @ 33hz with one, box was obviously too large because it sounded weak and hollow.
EDIT
Whoops, you did ask on MEA! My bad. Well, maybe try a series tuned 6th order....
But i don't see 140+ from the boot being a problem. I did a 3cuft box for a kicker L5 on 900w, got 139.8 @ 38hz in a VS, DD 9512 in my BMW 318i with NO fold down seat or ski port, 141.9 from 2400w...