I was honestly hoping to do more research with this before it got released/patched, but I will post what screenshots I have.
As the OP said, it is VERY difficult to land a strong enough helix. The helix needs to break roughly 125 damage to one-shot AV, with 9 modii. This requires int potions, int etudes, COR rolls, good gear, full merits, eseal, ebullience, weather, etc, etc.
Also, the formula breaks down as you apply many modii. The time remaining on Modus with fully merited scholars goes as follows:
Start: 50s (estimate)
Modus 1: 37.5
Modus 2: 28.125
Modus 3: 21.09375
Modus 4: 15.8203125
Modus 5: 11.865234375
Modus 6: 8.89892578125
Modus 7: 6.6741943359375
Modus 8: 5.005645751953125
Modus 9: 3.75423431396484375
However, I think the time remaining is floored at each step, resulting with:
Start: 50s (estimate)
Modus 1: 37
Modus 2: 27
Modus 3: 20
Modus 4: 15
Modus 5: 11
Modus 6: 8
Modus 7: 6
Modus 8: 4
Modus 9: 3
This can not be done without every scholar being fully merited. In addition, after over 30 attempts, we were never able to get it to one-shot AV. However, using 7 Modii, we obtained the following:
http://www.xzon.net/hanayaka/AV.png
Much more research has been done concerning this, but the hardest part is gathering 10 fully merited scholars (1 to cast the helix, 9 to modus). After literally, 30+++ attempts, we decided that one-shotting him is not possible. You will need to do bursts of 25% each, after locking his regen and benediction.
I wish everyone the best of luck, and hope I beat you to it.
P.S. - I'm not with OP, I had no idea other linkshells had figured this out. orz