#3 is out in the meat of the SI beam. The #2 is in the marginal fringe area directly under the boat. I am curious why #2 doesn't give as much relief to where you can see that the block is elevated in the DI image. I guess if you are shooting across the top at an angle you get some shadowing and the unit sees it as raised up, whereas if you are directly over the top it cant really tell that there is a difference between the top of the block and the lakebed. I guess that one could just be all silted in also, the portion that laps over from the bottom contour looks like it is a little softer.