Here is a way, we can make all the cap ships avoid the starabse by setting "Cannot attack structures" on all cap ships and cruisers. In this way, cap ships will always concentrate on the fleet attacking your antistarbase module (Orgov(TEC), Starfish(Advent) and Kanarak Assailents (Vasari,by giving it the range of Orguvs)). Concentrating fire on starbase would help little in any situation. But destroying the fleet protecting the starbase would give assault frigates a fighting chance.