To avoid either slumping or overarching in meditation, you need to get the height of your stool or cushion right.
But how do you know when you’ve found the correct height for you? There is no one right height that suits everyone.
Your own body height and flexibility will have a big effect on the height that is right for you.
The best way to find the right height is having an experienced person on hand to adjust your posture and give you feedback. It’s very hard to judge from the inside whether your posture needs to be changed. But here are some checks you can carry out yourself to see whether you are sitting too high or too low:
If you find you’re slumping when you relax then you may need to add some height to your seat or to increase its forward tilt.
If you’re using cushions, make sure you’re sitting towards the front of the cushions. If you sit towards the back then the cushions will provide a backward tilt, which causes slumping.
If you’re kneeling astride cushions and you find you’re slumping, try moving your knees slightly further apart. This alters the tilt of your pelvis and can correct a mild slump.