The Drop Ships Transport has a hangar bay designed to hold vehicles, not a docking bay, perhaps you are referring to another ship.
As far as carrying capacity, it is currently determined by comparing the weight and volume capacity of the larger ship to the weight and volume of the smaller ship/vehicle to determine whether or not the smaller can fit in the larger.
CR-90 Assassin-Class Corvette
Weight Cap: 2,500T
Volume Cap: 15,000m3
Has docking bay
So this ship can carry any other combination of ships so long as the total weight does not exceed 2,500 Tons or the total volume does not exceed 15,000 cubic meters.
Ship Rules Page