"whoever's in charge of the mailings ought to check a map, I also live about 300 vertical feet above the river "

One problem is that a lot of the flood maps are wrong. I've had to convince loan underwriters that some properties on high bank on Puget Sound waterfront are not in a flood plain. I've sent them a copy of the poster of the orcas swimming around the Space Needle and told them if Puget Sound floods the property in question, we'd have a lot more than their loan to worry about.
I've also used topog maps so if your lender requires flood insurance based on faulty flood maps, maybe you can convince them otherwise with the topogs.