Follow the Vandersteen instructions to get a general placement. The speakers need to be out from your wall at least 3'( if not closer to 4'). Using the instructions, divide your room up and use the measurement that gets them out at least this distance. You know, the divide by 3, 5 ,7 thing. Do the same for the distance from the side wall. Once they are set in a general location, measure their distance apart and set your listening position back approximately a foot from this position eg. distance apart 7 feet, distance back to chair would be 8 feet). Then measure to the listening point(acoustical center) to the chair. This needs to be about 8'. Any closer and the speakers don't have enough distance to blend. The speakers will actually look closer than 8' feet if you go from the centers. Now, set your tilt back about 1/4" MORE than the manual shows. Sit down and see what you have. If it doesn't sound right at this point, I would try another wall and reset. It should sound focused and pretty decent. You SHOULD NOT be required to aim the speakers at your chair or listening point. They should image well facing straight ahead or with a slight inward angle (about 5 degrees) If they don't, again, try another wall. If they have to be aimed at you or behind your head, something is not right.
you will have to balance the distance from the wall for best bass vs. best imaging. Without subs , that is all you can do. There will be NO perfect place that will yield best bass with perfect imaging and soundstaging. No speaker will. And people can call me nuts on this issue if they want to! You can get good but NOT perfect bass vs mids and highs integration.
Moving out from the wall should alleviate your bass boom. You also must place the SPL meter at the listening position at the proper height or you will get a poor picture of the actual frequency response. Also, you do realize that the Radio Shack meter has a few errors in the actaul response that are frequency dependent. A couple of points about 4 db off. However, you should be able to get a pretty good picture.
It took me about 3 months to get my 3A Sigs and pair of 2WQ's set up. It was very trying but worthwhile. Little 1" movements make a difference. Using the above should get you close if you are on the correct wall. Good luck!