To address this issue, we need to address the topic of "bass". Your sitting comfortably at home and someone drives by with a rather loud and obnoxious car stereo. The bass overpowers everything in your environment, and large objects start moving aroiund the room. Althought the car is "decoupled" from your space, the bass escapes it’s environment and finds it’s way into yours. The car is relatively "sealed", yet the bass finds a way out. It travels a hundred feet or so, penetrates your siding (or brick, or stone), sheathing, 4"-6" of insulation, 1/2-5/8" of drywall and rattles your brain. Long wavelengths with great intensity are difficult to constrain.
The second issue IS coupling to your room. Sympathic resonances caused by the vibration of your speakers couple with your subfloor, finds their way thru the insulation below, and through the ceiling material of the lower apartment. So, you’re actually dealing with two highly related actions here. YES, coupling will address one issue, but not all issues because high energy, long wavelengths are highly persistent.
The better question(s) are not so much WHERE the bass port is facing, but rather how low the tuned frequency is. Bass penetration is highly relevant to wave lenght. And, how loud you play.
As @ghdprentice suggested, getting to know your neighbors is the key here. You might ask them to help you discover the threshold of pain for them in THEIR apartment via your audio system, and establsh guidelines for behavior. You might discover that your music is not as intrusive as you thought.