Current game play does not compound the tower/miner percentage when using more than one modifier. Example: One scalar miner with a base speed of 13.3 and 3 mining modifiers with 41% increase each. 3 x 41% = 123%, This gives the scalar miner a speed of 29.536. This method uses the base speed of 13.3 no matter how many modifiers are added.

Compounding the percentage uses the updated scalar mining speed for each modifier added. Example:
Scalar miner: 13.3, mining modifier: 41%

1 modifier: updated miner speed is 18.753. If another modifier is added, use the updated miner speed of 18.753, not the 13.3.
2 modifiers: updated miner speed is 26.442. Continue using the updated miner speed for each additional modifier.
3 modifiers: updated miner speed is 37.283. So on and so on...

Compounding has added a speed of 7.747 and this is a significant increase, which will only prove more beneficial when upgrading the miners to the max level. This will also prove useful when using the power, damage, and attack speed modifiers.

G33K3R