Hi Rob
I am happy to hear that you are making progress. Your question as to why one hip is more “open, than the other is an interesting one. We are not symmetric. I too have my left hip more externally rotated than my right. But, this is not always something we need to fix. Sometimes it is just a result of the shape of our bones. But, if you are dysfunctional in some way because of your asymmetry, then maybe it does need to be addressed. The key question you have to ask yourself is “What stops me?, Why can't your right hip externally rotate as much as your left?
The “What stops me?, question is addressed at length in the first half of my book,
Your Body, Your Yoga. A brief description of this question is
here. And, if you like,
here is a video of me talking about this point (you have to scroll down to find my video as this is a post about a fascia congress with some other videos as well.)
So, what is stopping you? Is it tension? If so, your idea of more hip work could be beneficial. But if it is compression, if your bones are hitting and you are stopped because your right hip socket is more anteverted than your left, well-that is just you! You won't change that. However, in internal rotation (think of Eagle Pose with the legs) you may find your right hip is the “better, hip. Usually if we are very externally rotated in the hip, we lose some range of internal rotation and vice versa (not everyone, however. Some people are great in both directions, and some people are poor in both direction. This is discussed more in the book.)
So, what is stopping you? Where are you feeling the resistance? Based on that, you may decide you have reached your limit and trying to get more open/externally rotated will just start to hurt your knees. Practice with both intention and attention.
Cheers
Bernie