No, but I incorrectly divided by the stamina before calculating the chance, so I essentially added values doubly. Your numbers are correct.
I'm generally very lucky with bonus stages compared to other forum readers, but I had very good bonus chance experience with every event so far. On the last one I also had close to 90%. I'm currently 14/17 on bonus stages for the second phase of the event, so an 82% chance.
Updated numbers:
Regular:
Lv.50: Average 4356 (4184, 4800, 4368, 3112, 4384, 5704, 4704, 4000, 3952)
Lv.80: Average 4987 (4316, 4580, 4828, 5020, 5328, 5852)
Bonus:
Lv.50: Average 4716 (4820, 4740, 4548, 4684, 4788)
Lv.80: Average 9355 (8760, 9704, 9136, 9944, 9232)
50% 60% 70% 80% 90% 95% Lv.50 89.5 89.8 90.1 90.3 90.5 90.6 Lv.80 80.5 82.8 84.8 86.6 88.2 88.9