I paddle a low volume ski and am usually in rough water. I always use a wave deflector and have done so for years.
I have found the best position is as close as I can get it to the cockpit without hitting it with my paddle. It takes a bit of experimentation. I just tape it down so I can remove it easily if I need to transport the ski long distances.
Current boats
Epic V10L Ultra, Epic V9 Ultra, Fenn Bluefin, Nelo 600, 550, 520 & 510, Expedition Kayaks Azure, Mirage 732.
Previous boats
Spirit PRS, Fenn Swordfish, Fenn XT, Fenn Swordfish S, Think Zen, Epic V10L Club, Carbonology Sport Boost LV, Carbonology Sport Boost X LV, Fenn XT double.