Can’t see the image, so can’t comment on that. I can comment on placing your sub under your table (As you noticed that is a really bad idea, as you now have this big volume, low frequency, omni-directional speaker sitting under you). Stick them to the side, it really doesn’t matter much to the crowd. They won’t be able to tell what direction the lows are coming from.
As for the top end speakers sitting close to the wall and offering +3dB (not going into if this is actually a true number to begin with), that is only true for the low end (it bounces back from the wall and get’s added to the low coming out of the front. Since mid-high and higher goes only straight from the speaker, none of that is reflected off the wall. So effectively you are boosting your lows. There is an extra snag here though, if the reflected sound joins the original sound OUT OF PHASE, it will actually diminish the lows instead of boost them.
General “rule” is to keep speakers a decent distance from speakers, with the possible exception of low end/subwoofer units and only when you know what you are doing/know how to determine the right distance.
Also on a general note, keeping speakers in front of you is a good idea as well, even if you can only set them up next to your booth. This will help keep feedback down. Mind you, some rooms are so echoing that no matter what you do it will sound crap and/or produce feedback.
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