Well, just staying in your base to defend and do nothing else does not directly mean that your performance is good. Though, if you are a very good defender, then you do get rewarded a lot. If you defend 1.5 hours, that means 5400 * 1.25 = 6750 points. That's almost 14 captures. I don't see many offensive guilds who get that many captures during a WoE =/
If you were able to defend for 40 minutes, it means you did well and get rewarded for it but it also means you were not able to defend and you'll have to work harder to defend it longer or to capture it back (which will give points again).