See below for impedance plots of enclosure with two 4" diameter x 3.75" long ports. System tuned to 34Hz. This is as close as I can get to matching impedance peaks. The in-room SPL curve closely match the curve when using one 4" opening.
The math holds: doubled the port area and quadrupled the port length.
The sound feels a little over dampened right now. I'll likely pull out some of the fibreglass next week.