Seems like the mega gets pretty dark past 70 feet or so. Most of the images I have seen scanning 90 or 100 feet have pretty dark edges. Makes me think that 1200 really doesnt reach out that far even with the chirp.
I copied this from another thread.
455kHz Side Imaging provides 800 ft of side to side coverage.
455kHz Down Imaging works to a depth of 400 feet.
1.2 MHz Side Imaging provides 250 feet of side to side coverage.
1.2 MHz Down Imaging works to a depth of 125 feet