perhaps try leaning out more towards the outside of the corner. Your knees should be bent right over, and your legs leaning into the turn; but your upper body, from the waist up, should be right upright, horizontal. Your knees should be leaning in, but your shoulders should be horizontal. Like in skiing; or motocross. Watch any ski or motocross video as the proper technique is more visible in these sports than in mountain biking. But the principle is the same. Most on here will probably disagree with me, but I find the technique is exactly the same whether you're on a berm or a flat corner. The only difference is that on a flat corner, your tyres will wash a bit more, and you have to manage that. The technique though is exactly the same whether for bermed or flat. Also, make sure your line going into the berm is sufficiently high, a common mistake.