1st of all *which* WASC recipe did you use?
How much batter did you put in the pan - exactly what size pan and how much batter?
I'm very sorry to hear you have had problems. Yes, my *original* WASC recipe is based on the larger sized mixes so one must add more mix from another mix to make up for the loss. Not only have they reduced the size, but they have changed the type of rising agent used so we are all going to have to adjust and experiement until we find what works best.
Did you use wet baking strips or heat nail? I'm also wondering if your oven is working properly. It's possible something has happened there having had trouble w/more than one baked at basically the same time.
As for using a cake that has a dip in the center - you can fill in the dip w/icing before covering w/fondant.