The room comes into play in 1 vs 2 ports open. If the room is small there may be sufficient room gain that explains the 1 port open vs the 2 port open graph. I don't know what type of HPF or type of XO slope that is being employed for the 2 graphs. All this may also explain what is happening between the two graphs.
Klipsch RF 7 based HT 7.4, Pioneer SC 35, Acurus 200 Five, Dayton 18 Ultimxa Dual Sub Cab(2), Dayton 18 Ultimax Large Vented Sub Cab (2), on Berhinger I Nuke DPS amps, Aura Bass shakers, Samsung BDP F 7500, Asus/My Book Live HPC 4 TB
Yaquin VK 2100 amp, McIntosh XR 5 speakers, Samsung BDP F 7500