I think your back angle looks fine, you have a short upper body relative to the length of your legs, so you will be more horizontal than some in the bottom. I am built more like Cotton in "King of the Hill" only I have knees, so it is the opposite for me. It is hard to tell from this angle, but you might benefit from a slightly wider stance; maybe 1" or so wider. Some of the other guys on here can correct me if I am wrong. Make sure you are pushing your knees out.