To Calculate winning chance W:
X = A - B
=(Attack hero - Defense monster) - (Attack monster - Defense hero)
If X>0, W = 50 + (A - B)/1.5
If X<=0, W = 50 + (A - B)
Example: Hero N level 1 with Attack=42, Defense=15, Speed=32. Monster with Attack=43, Defense=13, reward $Gem ~1300-2600.
=> X = 1 => W = 50.67% => Estimate reward base on Speed, higher Speed, higher chance get more $Gem