Constructive Reflection.
We have to account for the placement of our speakers with respect to hard walls. The percieved issue is not necessarily a property of your speakers - save for the dispersion angles; rather it is about the geomerty of the room.
Your setup acquired constructive reflections closer to the rear of the room, while simultaneously suffering from destructive reflections up front. It's unusual, but not unlikely in a very hard surface space. This is especially true if the geometry of the room easily supports very simple reflections, and the surfaces have very little absorption, like structural glass and brick or concrete. When the distances are short, delay may be near negligible and we might not even notice where or how reflections are impacting our coverage. We may even appreciate the new reverberation and pat ourselves on the back for our fantastic speaker selection.
When a speaker is placed against a wall there is a +3db gain in low frequency energy. Placed in a corner (2 walls) we may get up to +6dB additional boost.
That's assuming we position the speaker correctly such that the reflections are constructive. The Bose 901 speakers are an example of a product where this property was an inherent design factor and installation
required a precise mounting relationship with a rear wall. Users who followed the instruction raved about the speakers and users who ignored the instructions were not impressed.
In a 'hard' surfaced room reflections are numerous and with little attenuation. In other words,
the room gets loud even at low amplification, but that loudness is not consistent across the space. Anywhere the reflections are constructive - it will sound louder. Destructive reflections obviously reduce the perceived level.
More specifically -
comb filtering is constructive/destructive interference at specific frequencies which is what most commonly occurs. The effect is most apparent to us with frequencies at which we are most sensitive (certain hi or mid bands) and we also tend to equate 'loudness' with lower frequencies because it is the lower mid and bass ranges that make it hard to have a conversation in the room. (Check the EQ in most restaurants running background music and you will find that it looks like an intermediate ski slope from about 500Hz on down, Removing all of the bass an most of the low mids is what makes it possible to converse in the presence of constant background music.
