Shards mana bases in limited

Anyone have any advice on creating a smooth mana base in shards sealed/draft? I feel like i'm doing a fine job of building, but i seem to lose to my mana base regardless of how good my deck is. Maybe it's bad luck, but I feel like I must be doing something wrong...so what do you guys think? What is the correct mixture of obelisks/panoramas/tri-lands?

Comment, please.