First of all if the 2016 had perfect flight you needed to add at least an inch of arrow shaft to get 2018's to fly straight with the same point weight and drawlength. Chad's right, if you want the 2018 to fly straight you need a 150+grain point. Not a lighter one. An easy way to tell if this is your problem is to overdraw your 2018's by 1-2 inches and see if this straightens out the flight pattern. Of course this will probably make you wobble when you release so everything goes back out the window.