Where s the bass?

Also keep in mind that Lower Freqs. have a longer wavelength, that allows them to travel farther away from your sweetspot.

IMHO the explanation of this phenomena (that incidentally
I was thinking about for few days now ) folowing the same
observation as yours is the following:
as Limabean observes, the lower frequencies have a much longer wave lengh that the other frequencies and in order
to reach a maximum has to travel accordingly that distance.
I understood that a full range trasducer with full bass
extension down to 20HZ ( not necessarly from recorded music,
but from an artificially generated recording/sampler as
the Stereophile Test Disc 2 or 3...)will reach it's peak
at about 40 linear feet traveling from the transducer.
I have a pair of speakers claiming such 20Hz reproduction
( Apogee Scintilla ) and indeed the sound in the 17' long
auditioning room doesn't reach the same bottom as the same
sound travelling through the open door another 25' or so,
right at the end of a corridor, were everythin vibrates and
shakes in burst of energy. I might be wrong, but that's my
explanation to what I've observed.

Definitely you need to work on your speaker/listening position combination. Accoustics do play tricks on us, get a test tone CD or select a CD with low bass information. (the best for me has been SPL+test tone CD)
Then select repeat of a small segment of bass info (hope your player has this feature) and walk through your room noting how bass intensity varies....
This will give you some hints on your room behaviour. Then try moving your chair/ speakers around 'til you get better bass. It will require patience!!

Sounds to me like Jadem6 has it right. Presumably your listening position is far away from a wall, and probably in an anti-node. In my large listening room I get a similar effect. If I move stuff around to fix the bass problem I get poor sound through the mids and treble - and even then I just get more bass, not necessarily better. I fixed the problem by adding two subs, after long and frustrating experimentation.