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, Carbonology Sport Boost X LV, Fenn Bluefin, Nelo 510, Fenn XT double, Nelo 600, 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