Quarter Wave box port area- going smaller than sd

[the mange]

I understand that a normal quarter wave box mimics a free air environment at tuning due to the lack of back pressure on the driver, but what happens when you shrink the port area below 100% of the cone's sd?

I'm tight on space working in a sedan's trunk, so I'm wondering if it's possible to make a quarter wave box that has a constant port area of like 25-50% of the driver's sd. I've seen it done before (with a reverse mount obviously) but I can't find it anywhere.

I don't intend for this box to behave like a proper t-line by fully dissipating the rear wave with stuffing or anything, I just want a quarter wave resonator that won't damage my driver or sound like a best buy set up.