I see that the AI has difficulty to deal with starbase...Also, I see them building starbases in area that I can just avoid to easily to defeat their fleet then I send theses torpedo bomber and GG...
Yes, the AI is both bad at attacking starbases and using them. You can easily lure it away from its defenses, and an undefended starbase is easily neutralized with the right countermeasures. You'll need to play multiplayer to live out a true siege battle in all its glory, the AI just can't do it justice.
Are the maps differents in each mode ?
Random-Small is the only one I'm aware of that changed. It got larger in Entrenchment (no change from Entrenchment to Diplomacy). It's ironically one of the more spacious maps now.
Since you're playing on Entrechment, I recommend the "quick-start" game setting. This conveninently begins with the capital shipyard and extractors already built, which effectively gives you higher starting cash since you don't need to pay for them. This really is a quick-start as a result.
