The box is small for this driver

Your system's −3 dB point is more than 1.5 times the driver's fs. A box always raises resonance, so some rise is expected, but this much means the enclosure is dominating the driver rather than working with it.

What is happening

The box air spring is much stiffer than the suspension. Since f_c = f_s\sqrt{1+V_{as}/V_b}, a box a tenth of Vas raises resonance by a factor of over three. The driver's own low-frequency capability is being thrown away.

You are also likely to be looking at a peaking response at the same time, since Qtc rises by the identical factor.

What to do

Either give the driver the volume it needs, or pick a driver that suits the volume you have. Which is available depends on what is fixed: a cabinet you have already built, or a driver you have already bought.

If the volume is fixed, look for a driver with a smaller Vas and a higher Qts. Small sealed enclosures want drivers designed for them: stiff suspension, heavy cone, modest motor. They will be less sensitive, which is Hofmann's Iron Law presenting its bill.

What not to expect from equalization

Boosting the low end electronically extends the response on paper, and it is a legitimate technique: it is what every DSP-corrected small subwoofer does. But the excursion the driver must produce for that boosted output is unchanged by the fact that it came from an equaliser, and it is precisely at the frequencies where excursion is already highest. Boost 10 dB at 30 Hz and you are asking for roughly three times the cone travel there. Check the excursion plot before committing to that approach, not after.