That makes sense. One of the wonderful things about these EP subs that no one talks about, is the fact that they maintain linearity even in a corner. You get maybe a 3dB boost in SPL in a corner but it's not a one-note boost.

Even though sound now is "bigger", it is not as articulate as it can be. A second 600 will help and you will hear the improved articulation.

House of the Rising Sone
Out in the mid or far field
Dedicated mid-woofers are over-rated