Started some of my own testing, which lets me pin down certain values that were ambiguous with Masa's data since I can choose the exact attack values to work with.
Test environment:
Nin/dnc vs Greater Colibri (slashing weapons, so no piercing bonus to factor out).
No spellcast, no gear swaps within a test.
93+5 str which gives 8 fStr.
Two d23 weapons. Final d on all attacks is 31.
Gear swaps only change attack (and dex/agi/etc, which I don't care about), not str or crit damage (so I can use the crit data later).
Can generally get around 100 attacks in per bird. I try to get at least 5 birds per level per test run for ~500 attacks per bird-level. With a d31 weapon, I should be fairly certain of hitting the damage limits, as well as seeing some of the shaping effects (though not so much on these tests, since cRatio is too high).
Testing for first bound factor: max pDif.
Whatever max damage result occurs, factor out the 1.05 multiplier in order to determine max pDif damage value.
Will list just the tests that gave useful results (other tests included all values that these tests covered, plus more, so don't actually contribute towards finding the limit).
Max pDif appears (from this and previous testing) to be a straight multiplier on cRatio. It also appears (from previous testing) to be capped, but I'm not trying to determine the cap yet, just the multiplier.
Code:
Attack Defense cRatio (1+ X/1024) Max observed Max/1.05 Mult. range (decimal) Mult. Range (X/1024)
464 322 1.441 (451) 56 54 +20.89% - +23.11% 214-236
464 327 1.419 (429) 56 54 +22.76% - +25.02% 234-256
472 327 1.443 (454) 57 55 +22.92% - +25.15% 235-257
489 327 1.495 (507) 59 57 +22.99% - +25.14% 236-257
Note: The multiplier ranges are calculated based on Max/1.05; they do not include the damage spread factor.
Reason for these values:
464 att gave a possible range of 234-236 when combining the lvl 81 and lvl 82 bird results. 472 was chosen to either prove or eliminate 234 (eliminated), and 489 was chosen to either prove or eliminate 236 (proven).
From that, we can see that the multiplier must be 236/1024 (assuming integer math in /1024 base), or 23.047%.
Masa's test data indicated that the max pDif multiplier was the same for 1-handed and 2-handed weapons. I have not re-tested 2-handed weapons, but will assume that it still holds for now.
Prior testing indicated that the multiplier had a max possible pDiff gain of 0.375 (384/1024, though I wrote 378/1024 in my notes; needs validation).
~ Gain: if you have 400 att and add 20% you end up with 480; the 'gain' is 80 points
The cRatio that would generate a gain of +384 would be 1.627. Testing 1.75 cRatio to see if it holds.
1.75 cRatio: 572 att vs lvl 82 birds. I put together a build with 571 att.
571 vs lvl 81 birds: 1.773
571 vs lvl 82 birds: 1.746
Expected max damage if gain is capped:
Vs lvl 81: 31 * (1.773 + 0.375) = 66 (69 after 1.05)
Vs lvl 82: 31 * (1.746 + 0.375) = 65 (68 after 1.05)
Expected max damage if gain is not capped:
Vs lvl 81: 31 * 1.773 * 1.23047 = 67 (70 after 1.05)
Vs lvl 82: 31 * 1.746 * 1.23047 = 66 (69 after 1.05)
Observed max damage for lvl 81 birds: 69
Observed max damage for lvl 82 birds: 68
Conclusion: The max pDif multiplier has a cap on the amount gained of approximately 0.375.
Caveat: Cannot necessarily assume that the same holds for 2-handed weapons.
With regards to max cRatio for 2-handed weapons: 2.25 plus the capped gain of 0.375 totals 2.625. Add in 1.05 multiplier and max pDif should reach 2.75625, which is close to, but not necessarily an absolute match for, the 2.76-2.77 max observed values.
On the other hand, the 20% multiplier value you use is clearly wrong (if it uses the same value as for 1-handed weapons), so can't be used as a basis for calculating max cRatio on 2-handed weapons. You'd end up with a max damage value of ~2.84 pDif if using the proper +23% multiplier on a max cRatio of 2.2.