-We have a resist chance = acting resists * 0.4
-We have a full resist chance = resist chance * 0.3 (1 - partial hit chance)
-We do a roll 0-100
-If our roll is greater than our resist chance then we return 100 which is no resist at all.
-else:
-if our roll is less than or equal to our full chance we return 0, a full resist.
-Else
-we return 100 * (roll - full chance) / (resist chance - full chance)
So basically the 30% chance we have to fully resist is stored at the bottom of our value. So as our chance to resist overall increases the chance to fully resist a partial spell increases despite that all spells are technically being resisted in some way.
Also when we do hit a resist because the end of the partial hit is beyond the scope of our roll the ability to make higher rolls diminishes. So not only is the chance to partial reducing but also the amount we partial for is reducing.
And so for your numbers I'll do them both:
250 = 100% chance to resist
1-30 = full resist
31-100 = partial resist
Your roll is 1-100 so you have a 70% chance to partial and 30% chance to full resist and if it's a partial you can get anywhere from about 1.5-100% damage on the spell.
400 = 160% chance to resist
1-48 full resist
49-100 partial resist
Your roll is 1-100 so you have a 52% chance to partial and 48% chance to full resist and if it's a partial you can get anywhere from about 0.8-46% damage on the spell.
That's using a spell that can partial hit which is quite a few but not all of them there are plenty of binary effects out there like slows and snares.
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