HMMMM interesting. Bodies will indeed reflect a lot of return, depending on the length of decomposition. During the later stages it will be less. Look at sonar images of bodies posted by sonar builders.
Cylinders will reflect signal but have a tendency to let the signal slide around and not reflect. Kind of like a stealth plane and radar. Round objects are like this.
Objects filled with air will let the signal pass thru the air and relies on the back of the object to reflect. Again look at this the same way as sonar and air filled water behind the propellor or the wake of a boat. Or in the area below a dam where water is being released.
I will have to look at this article.
First view of the article looks like a marketing write up. Farther in the article is talks about sonar and then shows a couple of bodies. having seen sonar and bodies first hand I have a bit of trouble with the statement. I think you will be fine with bodies search and sonar . However there are issues with getting a good signal to depict the bodies depending the other stuff around the body ....a flat bottom by itsself you will have not problem.
Chuck