I think point 2 has a big impact on stability. On a DF (Diamond Frame, I had to look this up) ride, you have so many degrees of freedom to use your body english to adjust to your stability. On a recumbent, it seems like you have much less you can do, and I wonder if instinctively what you might do could actually make things worse! For example, you might try to put your foot down or something because you feel like you're going down, and that will shift your balance even more. That said, I think with more miles you will gain more comfort and confidence in your abilities.