I do understand that the money/exp value of the mission offered right now take in charge the distance.

Thus, putting a distance slider is like putting a z-axis on a 2D engine

What about that:

The current sliders determine the money/exp (As actual) and the DISTANCE slider determine the RARITY (OR QL) of the offered reward... ?? [Something like Distance 0 = 3 QL under your current level and distance MAX = 10 QL over current? FAR FAR FAR]

Difficulty of the mission slider would have to not alter the QL of the reward but still the money/exp amount.

Think about it. Must of the time, the reward offered right now is just to sell it back. No real use.

Give it a though!