I sit tall and lean slightly forward to avoid getting left behind, point horse straight across ditch and use lots of leg to give him confidence and keep me secure on his back. No one I know recommends getting up in 2-point over a ditch. As soon as my horse takes off I give him all the reins he needs, letting them slip through my fingers. At the other side I quickly gather them up as we canter on.
Coffins, which have solid built walls (as opposed to ditches with natural sloping walls) would be ridden more like an oxer, in a 2-point position.
More ditch pics here if you are interested
Death Defying Ditches at Clonard Hunt | Facebook