This is purely speculation on my part as i have no knowledge of the impoundment, but it helps knowing these things to optimize those downriggers.
One of the interesting things about impoundment fishing is finding how deep they are holding and understanding the The Thermocline.
Hybrids are bred to withstand the warmer temperatures of these lakes. Bull shoals is currently at 78 degrees. This is way too warm for the larger striper whos preferred temperature range is 50 to 72 degrees. Stripers have been known to literally stack on top of each other on the bottom to avoid the high temps. Warmer water is also devoid of oxygen so stripers will search out moving water and cover and probably be close to the dams tailwaters. The hybrids on the other hand prefer open water.