when using economics "Use economics balance (requires economics plugin)": True,

when specifying the number 0.05, the calculation is not correct
is it possible to add support for minimum numbers
"Default structure damage cost": 

how many decimal places can you specify?

The problem wasn't the decimal places, there was a bug in the code that caused damage to be charged twice! I will be fixing this in the next patch. Just to clear the air, this is the formula for how the damage cost is calculated.

DamageCost = DamageDealt * CostPerDamge * (ProtectionPercentage)

So if someone hit a protected twig structure with a Rock, it deals 2 damage
DamageDealt = 2.0

If your config is set to 0.05 for the damage cost
CostPerDamage = 0.05

And the structure is 100% protected
ProtectionPercentage = 1.0

DamageCost = 2.0 * 0.05 * 1.0
DamageCost = 0.1

You can expect that 0.1 will be deducted from the balance.