User blog comment:Necor/How Stats affect our Servants' gameplay Stats/@comment-43554070-20190819084131/@comment-43554070-20190820020913

@Necor

NP gain is as follows.

Base NP gain per hit=Class Base Value*Deck Modifier*Mana Modifier/Arts card hitcount

Class base value is 1.5 for Sabers, 1.55 for Archers, 1.45 for Lancers, 1.55 for Lancers, 1.55 for Riders, 1.6 for Casters, 1.45 for Assassins, 1.4 for Berserkers, 1.5 for Rulers, 1.45 for Avengers.

Deck Modifier is 1.5 for 1 Arts deck, 1.125 for 2 Arts deck, 1 for 3 Arts deck.

Mana Modifier is basically determined by Mana parameter, which works the same way as Luck stat for star gather.

Note DW does not always follow this rule. They break it for servants they like allowing them to gain more than the formula indicated (e.g. Bride), and then some servants suffer by getting crippled gain way lower than the formula like Kiritsugu.

There is also a lose rule where no NP is allowed to refund more than 15% completely unbuffed (meaning no passives factored in as well). Servants who refund more than 15% will have their gain intentionally nerfed.

The formula for nerfing is as follows:

NP's NP gain per hit=15/(Card NP Value*NP hit counts)

Card NP Value is 3 for Arts NP, 1 for Quick NP. NP hit counts for AOE NP means hit counts against 3 enemies.

Perfect examples of victims from this rule are Atalanta and Berserker Lancelot, and for some reason the nerfed NP gain carried over to their face cards even though DW could set different base NP gain for regular cards and NP.

As I said it is a loose rule, DW has no problem letting waifus like Archuria (she breaks the mark even before her flat battery refund) and Rider Mo breaking the rule.

Source 1: https://www9.atwiki.jp/f_go/pages/1341.html (Japanese)

Source 2: https://bbs.nga.cn/read.php?tid=11004012 (Chinese)