Cam, sure personal preference is important, but yes, there's more involved. Contrary to some beliefs, the smaller the room the more the low bass area is boosted by room gain. This may result in the low bass being out of balance with the mid and upper bass and causing a boomy or excessively full effect. Axiom's Trim setting compensates for this by boosting the higher bass frequencies in relation to the lowest ones when the setting is Half or Full. In theory a very large room would give best results with the Flat setting, an average sized room maybe with the Half setting and smaller rooms with the Full setting. My room where I use the EP500 is slightly smaller than yours and I quickly found that the Full setting gave me the best bass balance. You should of course experiment and determine which setting gives you the best balance in your room rather than an unnaturally emphasized low bass.
Enjoy the music, not the equipment.