Reschke, it just doesn't work that way in the code. Each object placed on the map has an identifier or association, identifying the type of installation it is a part of. This is set by the person building the terrain.
Basically you have bases and you have strategic targets. An object can belong to either, but the code currently doesn't allow strat targets to be capturable. You could make a base look like a city or factory, but the code would treat it as a base; meaning it would be captureable, but would not effect the strat system. Basically, the code won't let you have it both ways.
The short answer is, the code won't let you make an installation that is both capturable and that can effect the strat situation. Hope that wasn't too confusing.