EV used the wall facing driver up to 300Hz. with a sealed enclosure, not vented. Reflexes back then were often boomy, and using a sealed woofer let them have greater control over the woofer loading at resonance. AR was beating the acoustic suspension drum around the same time.
I wouldn't run one higher than that, except corner loaded. The EV phase loading method is for against a flat wall, and it IS important the woofer be close to the floor/wall junction. I've tried the 4508 enclosure with the woofer in the upper and lower position, and the lower one is where all the "cool room effects" kick in, even with the bass boost turned off.

DON'T mess up a good pair of speakers to experiment with phase loading, since it is mainly for low freqs, and I will candidly admit that I have no idea how much of my subwoofer performance is from phase loading, and how much is just from having the woofer mistuned in a huge box.
Now if I had MADE UP MY MIND to run a woofer only to 300Hz., I would investigate the technique, if only for the reasoning of it's harder to DAMAGE a large cone that is facing the wall while playing ball in the house:( Damn, I'm SOOOO glad those jbl cones are TOUGH! Sam