I would say the alignment looks good because the shadows are perpendicular to side of target. If bottom was fairly level, you have consistent contrast on both sides of the picture. If the bottom were level and you get a brighter contrast on one side then the left-right alignment is off. But it is easier to evaluate performance on a known static target than fish. If the DI looks better, then chances are it is because the SI was improved because it is composed from the SI.