These are both Medium Mines, but something's not quite right... why do they make two different groups?
Oh, it's because they're technically different units. Wanna guess the difference? cormine2 is the Cortex Medium Mine built by everything that builds Medium Mines, and cormine4 is the one built by the Commando. For whatever reason, the Commando's mines have twice the buildpower cost. That is the only difference.
Why, though? Isn't the Commando already difficult to use as it is? Would it really be OP if it had normal mines?