Re: "stance of heaven (and earth)" and IS
Hi there to do with stance, in my training there a two, first called kamae with fee wide apart front foot slightly turner out with the heels in alignment, back leg only slightly bent with front leg well bent so you cant see your toes over your knee, this stance will be more identified by those who practice Yoshinkan style Aikido.
Second is simply hanmi, front foot forward toes only very slightly turned out or straight, slightly bent knee, rear leg points almost 90 degrees (if your right leg is forward) to the left, in what many call a T posture, with the back lefg slightly bent. The distance between the feet in comparrison to Kamae is at at least half the distance. Also the character HAN means Half, so HANMI means half stance, it also means you are showing half of your body to your opponent cutting down his options on how he may strike you, giving you an advantage. I beleive Saito Sensei (Iwama style Aikido) stressed the impoortance of hanmi over kamae.
Lastly a curve ball, there is shizentai, natural standing posture. Training like this in some ways is more realistic, in the sense you may not be in Kamae or hanmi when attacked, you would be in shizentai.
Oddly enough, if we examine our body movement when we practice aikido in fact we naturally move between all three,so to my understanding at the moment neither one should have more importance placed on it than another. However they should be trained and understood fully in there own right, only then can we see the illusion and truly understand no stance. In my humble oppinion.