Parameter Bonus (Dark Souls II)

The Parameter Bonus mechanics are a mechanic similar to the ones from the first game.

Also known as "scaling", it a rating, from E to S, of how well a weapon synergizes with a specific stat (most often strength or dexterity, but sometimes other stats too).

All the details are not completely known, in particular, how scaling works when there are multiple stats at once (such as for "quality" weapons).

Base damage
Unlike in Dark Souls, weapon scaling does not consider a weapon's base damage. The damage boost depends entirely on the stat, and the parameter. This has some ramifications:
 * Low damage weapons will benefit the most from scaling. In particular, weapons such as the Club will more than double its damage output. A Mundane Handmaid's Ladle can have upwards of 130 extra attack rating, when the weapon's base damage is only 10. On the other hand, weapons with high damage will benefit less from scaling. For example, a Giant Warrior Club will gain about +100 Attack rating, when it's base attack rating is roughly 500-600
 * Low damage weapons with high scaling (again, Club), will not benefit much from reinforcement: It will not increase the scale damage. Since the base damage is already low, it is (arguably) better to rely on scaling for damage, and save upgrade materials for weapons with low scaling, or high damage

Strength vs Dexterity
It has been observed that at equal rating, strength scaling will give about twice as much benefit as dexterity scaling. Or, to see it another way, dexterity scaling is equivalent to a "2-tier" lower strength scaling. For example, D scaling with 40 strength will give as much benefit as a B scaling with 40 dexterity.

Because of this, "quality" C/C weapons will gain more benfit from "40str/20dex" than "20str/40dex"

Soft caps
In terms of "return on investment" (for strength and scaling), unlike in Dark Souls, players get the "best" return on investment in the 30-40 range. The gains go something like this: Where "100%" represents an arbitrary scale of what you'd get per point, for a given rating.
 * 0-30 : 100%
 * 30-40 : 150%
 * 40-50 : 50%
 * 50-60 : 25%

In terms of scaling, it means the best gains are for putting all your eggs in the same basket, with either "40/20" for strength/quality or "20/40" for dexterity, but never "30/30".