It's very difficult to simulate dynamic riding positions while a horse is stationary, but Susan Friend gamely gave it a try for us on her Thoroughbred gelding, Felix the Cat.
1. Classic Cross-Country Galloping Position
Here, Susan is in the classic cross-country galloping position with her seat out of the saddle and her body quite forward so she allows Felix to gallop freely and cover a lot of ground.
Note that how far forward a rider gets depends on her horse's age, experience and balance. Felix is 12 years old and going Preliminary, so he can gallop in a fairly flat balance. As a result, Susan has her upper body quite forward. If Felix were a greener, younger or slower horse, Susan would need a more driving seat to keep him straight and balanced.
2. Rebalancing Position
About six to 10 strides from an obstacle like a coffin or a ditch, Felix needs to be rebalanced from the flatter, longer-strided gallop to a more bouncy, carrying canter, although again, the degree depends on his age, balance and ability level.
To assume the rebalancing position, Susan brings her shoulders back up over her knee, her hip over her ankle and, if he were actually galloping, Felix would follow her body weight back and rebalance himself without any fighting, pulling or loss of canter quality.
3. Jumping Position
Once Felix has rebalanced, Susan maintains the movement of her seat in the canter and lowers to the jumping position that she will maintain for the final four to six strides to the jump. In most cases, a rider's upper body should reflect the face of a jump (and her horse's body should reflect her body).
Assuming that Susan is approaching the vertical element of the coffin, she's keeping her torso a little more open, but she's not driving from behind the motion, which, instead of causing Felix to maintain a coffin canter, would cause him to become "impulsive" and push into her hand.
To learn the theory behind the coffin canter and how to introduce it in the arena, see the May 2008 issue of Practical Horseman magazine. And find out how to apply it on a cross-country course in the June 2008 issue.