I would like to revisit an earlier Spheres of Might build:
• 3rd-level technician with double hackbut: 8d6 base damage (Sniping's deadly shot: 16d6 damage)
• 4th-level technician with double hackbut: 8d6 base damage (Sniping's deadly shot with Combat Sphere Specialization: 24d6 damage)
• 5th-level technician with double hackbut: 16d6 base damage (Sniping's deadly shot with Combat Sphere Specialization: 48d6 damage)
• 8th-level technician with double hackbut: 16d6 base damage (Sniping's deadly shot with Combat Sphere Specialization and Vital Strike via retraining: 80d6 damage)
• 9th-level technician with double hackbut: 32d6 base damage (Sniping's deadly shot with Combat Sphere Specialization and Vital Strike via retraining: 160d6 damage)
• 12th-level technician with double hackbut: 32d6 base damage (Sniping's deadly shot with Combat Sphere Specialization and Vital Strike via retraining: 192d6 damage)
• 13th-level technician with double hackbut: 64d6 base damage (Sniping's deadly shot with Combat Sphere Specialization and Vital Strike via retraining: 384d6 damage)
• 15th-level technician with double hackbut: 64d6 base damage (Sniping's deadly shot with Combat Sphere Specialization and Improved Vital Strike: 448d6 damage)
• 16th-level technician with double hackbut: 64d6 base damage (Sniping's deadly shot with Combat Sphere Specialization and Improved Vital Strike: 512d6 damage)
• 17th-level technician with double hackbut: 128d6 base damage (Sniping's deadly shot with Combat Sphere Specialization and Improved Vital Strike: 1,024d6 damage)
• 20th-level technician with double hackbut (capstone): 128d6 base damage (Sniping's deadly shot with Combat Sphere Specialization and Improved Vital Strike: 1,152d6 damage)
Powerful round seems to actually be referring to size steps, at least at 2d6 damage and beyond, because the super-heated improvement earlier stipulates:
>one die step (1d8, 1d10, 2d6, 3d6)
The progression is atypical, however.