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....I think that D (and E) Deck balconies are 50% bigger than standard. Have a look at the picture below, which is of Ventura. I took this specially to illustrate this point. You can see five main balcony cabin decks: Riviera, A, B (all with standard balconies), C & D. If you look at the dividers between one balcony and the next, you can see that they're very short on Riviera, A & B, and much longer on C. On D deck, however, just above the boats, you can see that the divider is longer than on the top three but shorter than on C.
D deck balconies are standard size, completely overlooked but with a larger deluxe cabin. No shade if that side of the ship has the sun I'm afraid.