The Phalanx formula up to 300 Enhancing Magic Skill is well known.
Code:
Floor( Enhancing Magic Skill / 10 ) - 2
The -dmg tiers above 300 Enhancing Magic Skill are as follows:
Code:
-Damage Skill Level increase
-28 300 ---
-29 329 +29
-30 358 +29
-31 386 +28
-32 415 +29
-? 443 +28
-34 472 +29
-? 500 +28
I didn't test the damage reduction for the tiers starting at 443 and 500 enhancing magic skill, but at the moment I assume they are -33 and -35, respectively.
However, those are the exact starting levels I found for each new tier.
The skill level difference, if you start from 301 instead of 300, is 28.5 (truncating the .5's)
There isn't a commonly known formula for >300 skill Phalanx...
Until someone makes a nicer looking formula, here's my own one.
This works for a 301 starting point, with 28.5 skill between tiers and truncation of the .5's:
Code:
28 + Floor( (Enhancing Magic Skill - 300) / 28.5 - 1/57 )
You only need to subtract 1/57 (half of 1/28.5) or any positive number lower than it.
For simplicity sake you could replace the -1/57 with -0.01, and it will always have exactly the same effect.
Code:
28 + Floor( (Enhancing Magic Skill -300) / 28.5 - 0.01 )