Summary

This mod prevents level 1/2 of the Idiot Savant perk from being disabled while level 3's temporary effect (3x XP for kills for 60s) is active. I believe Bethesda's intention was to prevent the experience modifiers from stacking with the level 2 bonuses, however this reduces the average XP gain from the perk. Additionally, I merged in the various fixes from Unofficial Fallout 4 Patch (UFO4P). Other mods with the same objective use slightly different logic or miss off some of the fixes from UFO4P, so I figured I'd share my own fixes. Both versions below include the UFO4P fixes.

"Vanilla" Version

• Removes the "level 3 effect must not be active" condition that prevented level 1/2 from proc-ing. This occasionally leads to the level 3 experience modifier stacking with level 2 for a x15 multiplier to kills.
• Adds a "level 3 effect must not be active" condition in the IdiotSavantScript.pex script (source available) before the level 3 effect is applied to the player. This prevents the effect's timer from resetting if it is already active. 
  

Balanced Version

I noticed after some more game time with the version above that the x15 multiplier was occurring more often than I had thought (see the appendix for the details), so I implemented a more balanced version:

• Level 3 now provides 2x XP for 60s when Idiot Savant procs. The multiplier now affects all XP rewards, hence has been lowered slightly to balance it out.
• Level 2 is not prevented from proc-ing while the level 3 effect is active. The effect timer will reset each time level 3 procs and will always correctly reward 5x XP. When level 2 procs it applies 5x XP if the level 3 effect isn't active and 2.5x XP if it is, which then stacks with the level 3 effect to give 5x XP.
  

Note, the game engine does not allow you to apply an XP modifier to a specific source (such as kills, quests, speech etc.) while ignoring the generic XP modifier. By only using the generic modifier the resulting multipliers are be guaranteed to be correct. This version does not modify the IdiotSavantScript.pex script.

Installation

Install one of the above versions with the mod manager of your choice. Otherwise, I'm sure you know what you're doing.

Compatibility

• These mods are not compatible with any other mods that change the functionality of Idiot Savant (such as inverting the proc chance with intelligence scaling).
• Some mods that remove the "Yeah" sound may be compatible. The "vanilla" version is not be compatible with mods that edit IdiotSavantScript.pex.
  

Appendix

At a given Intelligence the probability of proc-ing Idiot Savant on any kill is p. The probability of proc-ing it on a possible combination of k out of n kills is p ^ k · (1 - p) ^ (n - k) and the number of possible combinations is nCk (combination notation). Hence, the probability of proc-ing it on exactly k out of n kills is:


Now consider how we get a x15 multiplier - Idiot Savant must proc on at least two out of n kills (within 60s of each other). Therefore the probability of getting at least one x15 multiplier over n kills is given by the sum of all cases where k >= 2 or equivalently:


For example for Intelligence 1 the probability of getting at least one x15 multiplier over 5 kills is ~1/10, over 10 kills is ~3/10 and over 15 kills is ~5/10. As you can see this is a little overpowered (and might be why Bethesda blocked it)!