I have noticed that everytime there is combat between an attacking fleet against a starbase and a defending fleet, then the defending fleet engage the enemy fleet way outside of the range of the starbase and thus mostly nullify the assistance of the starbase.

Please change it so you the starbase defending fleet to stay close to the starbase until the attacking fleet is close enough and thus be exposed to both the defending fleet and the starbases weapon. How it should work, imo, is that the defending fleet waits until the invading fleet is inside their minimum engagement range, which depends on what weapons the attacking fleet has, and only then start to engage the attacking fleet.