Brehan Crawford wrote:
... when standing with the feet side-by-side, say shoulder or hip width apart, when I tuck my sacrum underneath and relax the hips, making them level with the ground, my back straightens up, my head rests much more comfortably on my shoulders, and my knees naturally turn to be in line with my feet, instead of turning in as they usually do. This is what I was taught in Tai Chi and have read in numerous books by people that supposedly really know what they're talking about.
When one foot is in front of the other, as they are in a hamni stance, my hips tend to want to rock forward a bit and my butt tends to stick out a little but I try to not let this happen. I find that keeping the sacrum tucked helps me initiate movement with my hips and shift weight easily from one leg to the other.
I think what you are saying is tilt the hips up (sacrum underneath), which goes against what some others have been saying. I also think that the hips should tilt up. To me, down is wrong. In this respect, many arts are the same (even though they are often not aware of it).
When standing normally the hips are neutral, neither back nor down, but on meeting your partner to make technique they automatically move up to solidify the connection somewhat between the upper and lower parts of the body - it also straightens the back. In fact, I sometimes call it undendable body.
Try this lie on the floor and press your tummy up - shoulders and heels on the ground. See how your hips are. This is part of 'my' unbendable body training
The stand up and make the same thing happen when meeting uke. It will help your understanding no end. Well, it does for me.