Ovinomancer
No flips for you!
Yup, I was using .5 for the total hit chance instead of .55. Same numbers for your level 3, but we still diverge for 7 and 11.Your made a small error here. I think at AC16 your numbers for a Rapier would have been correct.
With +3Dex and +2 proficiency vs 15AC you have a 50% non-crit hit chance (10-19 rolled) and a 5% crit chance (20) and a 45% miss (1-9 rolled).
Numbers underlined and bolded below are the difference:
Case1:
CASE 1 (non crit hit) 0.7
--case 1a -- first non-crit hits, second misses -- .5*.45 = 0.225
--case 1b -- first misses, second non-crit hits -- .45*.5 = 0.225
--case 1c -- both non-crit hit -- .5*.5 = 0.25
.225+.225+.25=0.7
Average damage Case 1: 14.5 * 0.7 = 10.15
Case 1 + Case 2 average damage: 10.15 + 2.535 = 12.685
For TWF
Case 1 -- 1st non crit hits, second misses - 13.5*.5*.45=3.0375
Case 2 -- 1st misses, second non-crit hits - 10.5*.45*.5=2.3625
Case 3 -- 1st crits, second misses - 24*.05*.45=0.54
Case 4 -- 1st misses, second crits - 21*.45*.05=0.4725
Case 5 -- both non-crit hit - 17 * .5*.5=4.25
Case 6 -- 1st crits, second non-crit hits 27.5*.05*.5=0.6875
Case 7 -- 1st non-crit hits, second crits 20.5* .5* .05=0.5125 <--- This is where the TWF really loses damage
Case 8 -- both crit 31*.05*.05=0.0775
Total=11.9400
I get ADV 20.7675 and TWF 20.73 for level 7, and ADV 29.4 and TWF 30.35 for level 11.
At level 7, overall hit chance is .65, DEX is 4, and Sneak is 14. At level 11, overall hit chance is .75, DEX is 5, and sneak is 21. These are the only changes happening. The effect on crit chances for TWF is still present -- it shifts dramatically towards both hit 1 crit. This is the same spreadsheet that generates you level 3 numbers and does so when I corrected the base hit chance from .5 to .55. So, approach was correct, data entry failed.