While discouraging I will say even regular Napa Rose Dining is amazing. Also keep checking back for Chef Counter especially 24 to 48 hours , even same day at opening doesn't hurt to ask ! Just remember it's currently only Fri- Sun which creates high demand. Speaking of which , I have a reservation for the weekend of Sept. 2nd , when are you going as I may need to give it up ?
Riverbelle Premium Fantasmic is hit or miss , the regular packages seem to be great as I've done them recently. Keep in mind the Premium with seats is only about 7 or 8 tables so that is one of the hardest to get. Otheriwse just book River Belle and ask for the package at check in

As an alternative , I watched the second show of Fantasmic seated at the food area just adjacent to Harbour Galley across from Haunted Mansion.
Basically an expanded seating area so got a closeup view with seats mind you , of the floats and even saw the dragon , Mickey , projections , etc.