Fix log access for target_key in sweep.py

[ClashLuke]

if cost > 1.2 * self.upper_cost_threshold:
    return 0.9 * self.max_score

This check doesn't work if the numbers have a nonzero offset, as the offset is scaled as well. Most visually, if I have a negative score, it will push the target up toward zero, instead of down into an easier regime.

The intended code is likely closer to max_score - 0.1 * (max_score - min_score)