Rich dip at 3,7k probably vanishes if you move your load limit closer to 1.0 in that area.
Lower = leaner. In terms of "ecu picks a cell further on the left"
If the engine doesn't respond to it, I think the maf scale is probably off.
Regarding that lean spike around 4,1k, I'm not sure.
It looks like the afr curve follows the shape of the exhaust cam. Coincidence?