Hey @armagash,
The rewards from sieges aren't easy to get, you've to do kills on your own, and not from a group or alliances, if you're in an alliance all of their kills count in that scoreboard but sadly they aren't counting for your GP contribution, also the siege zone has a limit and most of the time asmos or elyos are outside of it. Also using ap boost from the item-shop can help you a lot
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I hope I've clarified your question.