Need help downsizing my box

I upgraded my box from 1.8 cubic ft to a 3 cubic ft for my rockville 12" destroyer but with this new box i purchased i feel like its not giving me that punch on the low decibels like the other box but the Mid bass sounds a lot better but i need that punch. The speaker for a vented box says 2.84 cubic feet vented. I would prefer not cutting the box. Can i add that can foam in a section of the box to take away cubic space?what should i do? Thank you!
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Sony XA-5400ES SACD
Pass XP-22 pre, X600.5 amps
Magico S5 MKII Mcast Rose speakers, SPOD spikes
Shunyata Triton v3/Typhon QR on source, Denali 2000 (2) on amps
Shunyata Sigma XLR analog ICs, Sigma speaker cables
Shunyata Sigma HC (2), Sigma Analog, Sigma Digital, Z Anaconda (3) power cables
Mapleshade Samson V.3 four shelf solid maple rack, Micropoint brass footers
Three 20 amp circuits.
Sony XA-5400ES SACD
Pass XP-22 pre, X600.5 amps
Magico S5 MKII Mcast Rose speakers, SPOD spikes
Shunyata Triton v3/Typhon QR on source, Denali 2000 (2) on amps
Shunyata Sigma XLR analog ICs, Sigma speaker cables
Shunyata Sigma HC (2), Sigma Analog, Sigma Digital, Z Anaconda (3) power cables
Mapleshade Samson V.3 four shelf solid maple rack, Micropoint brass footers
Three 20 amp circuits.
Game Room HT: Denon AVR-X4200w; Sony UBP-x700; Definitive Technology SM450; Definitive Technology LCR2000; Definitive Technology StudioMonitor350; Mirage Nanasats; Sub - HSU VTF-2 MK5
Master Bedroom
Cambridge Azur 551r; Definitive Technology promonitor 800; ACI Titan Subwoofer