room setup suggesion needed

How important is back wall setback for the front ported speakers ? 

As @newfzx7 mentioned, you will get less bass reinforcement for all speaker types by moving them father away from the back wall, but the key is finding the position where the speakers sound most balanced and the bass blends best into the sonic picture.  Obviously playing music with more bass content will be more helpful in readily hearing the differences in placement with this aspect, but do also play music with big recorded 3D space so you can also better assess critical imaging and soundstage differences as well. 

Large Room for Small Audience is Difficult (you or you and a mate/friend perhaps)

Square Rooms are Problematic

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My suggestion, use the room differently, sub-divide by use, not necessarily walls, although tall folding screens might work): perhaps move the music area 14 feet from a wall, use the 14 x 30’ area portion for: (semi-private office, music library, conversational seating, small video, dining, a combo .........)

now the music space is 16’ x 30’.

I would first try:

speakers on short wall, a few feet from sides (one side a wall, other side a tall enough bookcase (lps?) to 'be a wall' to the speaker

far in front of rear wall. now rear ports not muddying initial reflections, and you will get a deeper sound-stage.

Speakers: Wheels: Alternate Locations

Toe-In Alternates: Stereo and Video

To read photo captions, and/or view larger photos (any virtual system), top bar, ’TOGGLE FULLSCREEN’

One tool that's super easy ot use is the AM Acoustics room mode simulator.  Plug in your room dimensions and it will help you avoid the worst trouble spots for speakers and listening location.

@elliottbnewcombjr I had a very interesting phenomenon, I placed 2 floorstanding speakers next to my standmounts, about 5 inches on the outside. The sound of the standmounts has completely transformed, it helped the speakers disappear and made the different elements feel more focused, "sourced".

grislybutter

Interesting, that's far more than subtle acoustic change resulting from a relatively small physical change