The reference point for an unplayable ball is the ball. Golf depends on the integrity (and knowledge) of players to establish the proper relief area. Again, with the LCP exception, the only time a ball must be marked is if it must be replaced.
Here’s another silly rule that could inadvertently cause major problems. The rules also contain an optional local rule, like LCP, that is Lift, Clean, and REPLACE. I have not seen that one used yet, and I will never put it in the events that I do for colleges, etc. My guess is that it was put in the rules to satisfy the R and A guys who remain opposed to LCP in any conditions. They want everything to remain strictly to play the ball as you find it. Try to enforce that with today’s entitled tour pros.
Good luck with that, especially in events like the World Am where most of the guys never play in any other competition and regard the rules as suggestions. I usually inform my group that I am a certified rules guy so they can ask me any questions. That saves a lot of trouble during the round.
The relief area for going back on a line is only one club length, not two, another misconception among players.