It not complicated. Nor is it a bias. Those are actual numbers out of your script.
On average, both methods require the same number of steps to reach a solution.
Noo,
If we take these metrics into account, it only means that, approximately within that key range, the prefix method achieved a higher success rate, which is highly significant.
dividing keys(avg) by wins, you'd determine the average success rate.
keys(avg)/wins = success_rate(avg)