Yes, but the PO's box is already too large so it would not help his situation.
"too small" is if the Q is higher than .7 or so. Not subjective. Physics. OK, I'll give you .8 for acceptable ripple.
If one really wants to lower the F3 of a driver via cabinet alignment, a BP-6 can do it, but with an 18 inch JBL, only use I think of is for talking to elephants or submarines.
If lower F3 is your only goal, look into a Linkwitz Transform.
