Is it the soak time?
I am very new at this but I have slumped in a similar mold several times in my class. The instructor told me that longer soak times are required to get slumps to fill corners well. I’ve not had the curved sides issue. If the temperature of the class doesn’t equalize properly, it will slump unevenly. Soaks at various temps are supposed to fix that. I’ve been experimenting at home with ramping up in stages with short soaks to allow the glass time for the heat to even out. Maybe someone with proper expertise could elaborate on this.
Flee at webetilin’ Studios