We went last Wednesday night, did the reserved dining at Ariels grotto. Managed to get a spot right in the centre of the red line (front rail elevated) Hydroguy suggested and had an awesome view. I thought it was better then Fantasmic and advise people to make the effort to see it

Almost half of the red line (front rail elevated) area is now reserved for wheelchair seating. Make sure you don't stand in the chalked off area or they will ask you to move out. Just as the show starts people are allowed in there behind the wheelchairs, but your view may be impeded by their companions.
I'd advise get there 90 mins early as Hydroguy suggests and
make sure you know where the corral for preferred diners is so you can hop in the 'queue' that the CM's swear doesn't exist for preferred diners as soon as they put the ropes up. The CM's wouldn't give us straight information about where the corral and queue formed for preferred diners would be and we almost missed getting a good spot despite being there well in advance to 'queue'. It was luck and a 'honest' CM meant we didn't miss out in the end, and it was the favourite show of 4 out of 5 of our family. I know I would have been annoyed after spending alot on that dinner if we'd listened to their advice that we'd all have a good view and to come back at 7.45 because theres no way known myself at 5 foot 4 in height or my kids would have seen anything if we weren't in the first two rows on a level.
If you have really small kids or are not capable of holding them up for the whole show you may prefer the front rail wet zone area, as we found a couple of really tall men stood in front of us in that area with their older kids on their shoulders and that blocked our 4 year olds view so my hubby had to lift him up and our 9 year old had to stand in his pram to see. We may have just been unlucky on our night but if you don't want to risk it I'd aim for the front rail wet zone, which is where I'd head for if we were going again.
Thankyou for the advice Hydroguy, it meant we saw an amazing show in the best possible place to view it. It really was a highlight of the holiday