Nice job, where did you get this unit from?
FWIW, I shoot thru Hull on my kayak, and have my puck directly in water on my boat, and haven't noticed a trememdous difference in the reading. I use the same FF/GPS on both kayak and boat, each have their own puck. I wish more kayak manufacturer's would just build an independent puck area on the bottom of the kayak in the mold, and not be a part of the kayaks scupper system.
chris