RESURRECTION.
If anyone gets to here from reddit/google its worth noting that the issue above is quite simply happening befause the body is - as always - attached in place to the capsule.
You have to apply the offset of the lowest foot to the hip so that the character slumps down, set that foot to 0 so it isn’t adjusted, and the other foot offset should just increase on its own.
if you want to be technical, the increase is the same amount the hip went down. Technically you could calculate all the positions in 1 go, which makes any IK much smoother then when you try to let it auto adapt since the next offset will happen in the next frame…