Here are a couple pics of step 3 in progress. Obviously the scale is non standard so you can see what is going on. In practice I was looking a couple octaves higher to get a wider picture of the level of the main speaker by scrolling.
First, sub plus one speaker, no smoothing. Is the main at target or not?
Now with 1/2 octave smoothing it is fairly easy to see the main is below target 3-4 db. Note, there is more influence from nulls, so I probably adjusted the level up about 3 db not the full 4.
Also, the null at 80 and 140 or so is probably a phase issue, so I am ignoring those at this point and will correct with the delay setting later. The details of that are another topic but I think most will get the point.