Not much time to work on this, but here is a sketch of the kind of thing I have in mind. Sorry for the clumsy examples.
Skill: Acrobatics
Use: Balance
Mundane (TN10): Walking a 1' wide board laying on the ground
Average (TN15): Walking a 4" wide board 10' above the ground
Hard(TN20): Walking a 1" tight rope in calm weather
Challenging (TN25): Walking a 1" oscillating rope in calm weather
Heroic (TN35): Walking a 1" oscillating ropeĀ with strong winds
Legendary (TN45): Doing somersaults on a rope with strong winds
Does it make sense ?