I've used this with an E.C. in support of a LOMA request
I imagine they will come up with a HEC hydraulics profile that the computer spits out to the nearest 0.01 feet, and the accuracy could easily be off by a foot or more, as you know. Anybody who has done HEC analyses to the best of their ability has done multiple cross sections in the area of concern, and upstream and downstream in the zones of influence (which are also variable), made tailwater measurements, and then calibrated the model. One cross section submitted by email, and a few pictures either leads the computer operator to use very conservative n values which raise the level artificially higher than it should be, or they just plug in the recommended values and don't worry about it. I would not touch this technique with a 10-foot pole.
I was asked to hire a public adjuster who would arrange the meeting with the insurance company and file the documents required.