When I stuffed a loudspeaker box (yamaha 3 way with 8" woof), I put too much in it (it wasn't packed it but there was alot). On my receiver (with loudness button on), my usual setting bass is -4db.
I had to increase bass to 0 to give same bass with all that extra pillow fill.
I pulled a bunch out, sounded better, and more bass than totally filled.
Then I pulled more out so there is less than I'd expect, midbass semmed better and back at -4db setting on the knob, mids improved compared to empty box.
So moral of the story, I'd not make a box smaller and then use fill to make it seem larger. Add some fill and listen, add/subtract and listen, etc.