When designing a ported enclosure to be used as an isobaric setup, do you just use the same T/S parameters except for halving the Vas?

Or alternatively, using the T/S parameters to design a ported enclosure, and then using half the volume, but still porting the enclosure at the frequency recommended for a full sized enclosure?

For example. I want to use a couple JL Audio 12W6's, and the computer program says that for a flat response from a single driver, I need a 7.87 cubic foot enclosure ported at 19 Hz. If I'm going to mount both drivers face-to-face, should I halve the volume, but still port the 3.94 cubic enclosure to 19 Hz?

That seems like the logical thing to do, but I was just curious if there was someone that knew for sure. Thanks in advance.

And for those that are wondering why I would build such a thing...I've built subs like this before and they sound amazing. When your subs can play flat down to a -3dB point of 17.94 Hz (out-of-car), you hear things in ways that you've never experienced before. The recommended enclosures are usually designed with trade-offs (smaller enclosures produce peaks and sacrifice bass extension). There's no such thing as one-size-fits-all.