Zhuang Zhan IS just upright standing with the arms somewhat spread and curved (palms towards your body). The correct posture is not a specific frame, but about getting the principles right. The arms could be high or low. The legs almost straight, or quite bent. The torso is upright. The neck is distinctly under NO STRAIN. The back is relaxed (I like the "Wu" style comment, "the buttocks droop" to describe how /little the pelvis is curled forward and the lower back is loose and alive. The belly is like a large bowl containing water to the brim and not spilling it.
Standing requires:
10 to 20 minutes like this without distraction (actually, I remember Ying Jun saying that just getting into the right posture for a FEW SECONDS can be beneficial). Daily. Put the mind on the dan tien - ie, not on anything else.
Standing this way HURTS the thighs (after a minute or three). No hurt means not Sung. No hurt means body/posture broken and held by tension. After you get this, things get painful (more sung, more pain) and more interesting. You get stronger and more extensively strong (ie, in any position).
Sung is a kind of relaxed "giving of your weight" into the ground (maybe "rooted"), but at the same time YOU coming up out of that ground. The "Dang" (groin) rounded, which means something like you are supported by an arch involving your sacrum and trochanter like an arched bridge support. [Different teachers have different detailed geometry - indeed, Chen varies the position as the person gets stronger and more "like a mountain"].
If all goes well (muscle burn, remaining relaxed, but no cramping from tension), after several months, you also work on Dan Tien Rotation (see next). This is where you maintain Sung but shift position. Your attention is on the Dan Tien, and you INTEND to move it. You move because you intend to move your Dan Tien.
Like a mountain. Don't lean. Be upright. Don't collapse downward, but send your weight vertically downward, through relaxed muscles (thighs, back, all joints like ankle, back of knee, front of thigh crease, behind waist, solar plexus, neck, ALL soft and almost open, but not quite). Your belly not hanging out. More like a pot holding your guts (but not squeezing them). Arms feel a bit "springy outwards". Front not stretched. All tension leaves the top of the body. Practice with ease and subtlty. If thinking too much (an occupational hazard), *just* stand and breath naturally.
A lot of what seemed to be going on in corrections for standing reminds me of the "feeling your collar with the back of your neck" which Wei Shu Ren referred to. See Jarek's website translation of some of Wei's material here.
Tom Osborn