Sorry for the confusion on my wording, what I meant by that was it was learned thru the Aum, not that it is an Aum heh. my bad.

Well, some numbers.
Stats: Level 46, Dexterity 391, +21 parry, +46 dodge

1. Buffs: None
18.90% melee evasion (7.74% dodge, 7.47% parry)
Diffrence: Bonus of 3.69%

2. Buffs: Aum Ti
23.28% melee evasion (7.74% dodge, 12.47% parry)
Diffrence: Bonus of 3.07%

3. Buffs: Eternal Crane Stance
32.34% melee evasion (15.74% dodge, 15.47% parry)
Diffrence: Bonus of 1.13%

4. Buffs: Crane + Aum Ti
36.34% melee evasion (15.74% dodge, 20.47% parry)
Diffrence: Bonus of 0.13%

5. Buffs: Reed the Wind
62.85% melee evasion (57.74% dodge, 7.47% parry)
Diffrence: Penalty of 2.36%

6. Buffs: Aum Ti + Reed the Wind
64.86% melee evasion (57.74% dodge, 12.47% parry)
Diffrence: Penalty of 5.35%

7. Buffs: Eternal Crane + Reed the Wind
72.49% melee evasion (65.74% dodge, 15.47% parry)
Diffrence: Penalty of 8.72%

8. Buffs: Aum Ti, Reed in the Wind, Eternal Crane.
74.11% melee evasion (65.74% dodge, 20.47% parry)
Diffrence: Penalty of 12.10%

Quick conclusion: The bonus drops rather linear (someone better at math can probably correct me) down at least down to 62.85% (so one could actually assume the soft cap is at 65%) but then the penalty goes really rampart.

Updated conclusion: It appears the the real penalty starts around 60% and then VERY rampartly increase. I would suppose the actual cap (where any bonus has such a heavy diminishing return it reach 0) is around 80%, maybe tops 85%. Some harmonious and/or drunken with a good martial sword should be able to reach it.
There does not appear to be a cap for the indidivudal skills involved - the diffrence between example #5 and #6 would prove this.

so the cap is on  dodge and parry, can you try aum liat + crane then reed

Also, now that I actually read your sentance over and understood the question:

Base + Aum Ti + Reed + Crane:
7.74 + 0.00 + 50.00 + 8.00 = 65.74.

Of course, it might be cutting off at a certain %, but that dosen't explain the generally decaying bonus (unless there's an UI bug - naturally). Someone with a big martial sword could probably present numbers where dodge isn't as extreme (ie high evasion with a large influx of parry, rather than the rather low I have) and that would solve that mystery.

Drats i thought it was great gettting 80+ percent with aum liat, reed, martial sword and eternal drunken swagger. But 65 is the actual cap? A slap in the face for drunken then tyvm!

I checked Nusibe tonight between zone in and godking room and nothing.

The soft cap is somewhere between 60-65% either from stacking issues or because of a cap. Dodge and parry have seperate caps (to an extent) example: if you have a lot of +dodge, instead of gaining more +dodge, and piece that gives +parry will provide a greater benefit. This also applies to which Aum you use, dodge or parry.

Absolute maximum I've able to gain so far was 86% (with 1min evasion buff from drunken master quest), after a little bit more gearing I've been able to maintain around 84% (buffed). Incredibly hard to acheive much more then 76% (requires sacrificing of stats for +evasion/+dodge/+parry). After around 70% you seem to only gain about 1/3 of the benefits for evasion buffs / gear. I imagine this keeps scaling to the point where 95-100% will be impossible.

With that said, many factors apply beyond the evasion given to you in character screen. It applies to auto attack damage of equal level mobs. Abilities often have a higher (or lower) accuracy rating which will upset your percentage, as well as mobs over your level, as they will have level advantage on you. Same reason why your evasion/mitigation % goes down when you level, it rescales to the next level of mobs.

So even with 100% evasion, expect to take some melee damage. I think Reed in the Wind was a great fix for monks role as puller / offtank. Has a good cost / benefit relationship and something like this was definately needed. Great job by the dev team to give us a useful ability and thank you.