It's very hard to comment on a test without knowing the details of a test.
I can guarantee that short of finding some doldrums (glass flat ocean with no wind) that extend for 9 miles and then doing very sensitive calibrations and THEN doing a test, I dunno how that test could possibly be done over water.
Also, think of this... IF the earth were flat, we wouldn't need satellites. We could simply host large structures with lasers and mirrors on them to send messages and even at 3 times the distance, the latency would still be significantly lower than any satellite based communication.
All things being equal, our little oblate spheroid that is a little fatter than it is tall, is basically a sphere as others have said, but it has plenty of curves. As 503 pointed, there are tides, which due to soil liquefaction also affects the height of land in some cases. I can guarantee you Florida is affected by the tides to a degree.
Anyway, without any data on the test, it's hard to address where the test went wrong or to explain how the science generated such a result.