Hi Dean,
For starters, see my post in the "tweaks" section. Fifth down from the top.
A few of other suggestions regarding positioning:
1) Try setting the rake (vertical) angle of the panel so that it is perpendicular or 90 degrees from the floor. Regardless of whatever rake angle you end up with, make sure it is exactly the same for both speakers.
2) Same applies to toe in and distance from back wall.
3) Try to get four to five feet of distance from the panel to the back wall. If this is impractical, maximize as much as possible. A minimum of two feet is desirable from the outside edge of the speaker to the adjacent side wall. Also, minimize placing objects (TV, cabinets, furniture, etc) between your speakers and the back wall.
4) Be patient and experiment. The SL3's are great speakers and will reward you if optimize their placement and address any room issues with proper acoustic treatment.
GG