Being a continuous occupy of BC cabins, we have never had a problem with the Deck 13 cabins or the forward section of Deck 12 with obstruction of full sun to the balcony.
Yes, those cabins on Deck 12 from the Sun Deck staircase by the Pavillon Pool and far-est cabins to around ex. 12028 does have lip from the Sun Deck Partition..
But from ex. 12028 to Forward are open to full sun. Except when you get closer to the front,
you will be obstructed by the Bridge Wing sticking out.
We are careful when booking cabins on Deck 12 when booking. And because Deck is so far to the front, we opt to past them up for stays.
Also, the walkway above Deck 13 never bothered us during our 14 day sailing even with people standing up there.
Your choice....