Enclosures have two purposes:
1. Isolating the front of the speaker from the back of the speaker to prevent cancellation at low frequencies
2. Modifying the suspension of the speaker to achieve some target Q
The suspension operates mostly below resonance. At resonance, nothing is very good at controlling the motion of the moving mass (that's what resonance is) and above resonance, the motor controls the motion.
So, the box affects the speaker around resonance, but that resonance is Fc rather than Fs. There is no Fs for a speaker in a box.
So, if you're going to use a high pass filter, you should cross above resonance to minimize distortion. If you're going to follow this basic rule, then the box makes sense ONLY if you need it for purpose #1 above. If you don't need it for that, then it's better NOT to have an enclosure, because Fs is always lower than Fc.