Fill the whole bass trap with lower density earth wool.
Contrary to direct logic, the higher density is not better for absorbing bass,
lower density and
depth together is what you need. This is common practice in recording studios, its variations are often called a super chunk bass trap.
Thinking higher density is better for absorption and using too much is also one of the reasons people do not like the sound of absorbers in their rooms. They use high density materials and end up loosing more mid and treble then they like. They blame the absorbers and end up thinking acoustic treatments make the sound flat and lifeless, but the reason was actually wrong application of absorbers.
If you have further question maybe pm would be better. This has become a conversation and maybe it is better to continue that way