My goal is to make an object that increases a player's stats by a series of factors. If we take Intelligence as an example,

I would like it to SET the base number to 14. 

Modifier -> SET ->  INTELLIGENCE SCORE -> 14 (Fixed Value) 

But then I would like it to increase by whatever the player's proficiency bonus currently is (so +2 and player levels 1-4, +3 at 5-8, ..., +6 at 17-20)

I have tried ... 

Modifier -> BONUS -> INTELLIGENCE SCORE -> PROFICIENCY BONUS (Additional Bonus Types) This seems to not do anything at all, perhaps I am using this option incorrectly? could it be used to increase a character's proficiency bonus by a fixed number? if so why? 

Modifier -> Stacking Bonus -> INTELLIGENCE SCORE -> PROFICIENCY BONUS (Additional Bonus Types) This also seems to do nothing .... 

Currently, I am all doing this as an item, but I would also be willing to do it as a Feat or Spell if I thought it would make it work better. Has anyone attempted anything like this? and actually got it to work? 

any one have any ideas? 

If anything would work, it would be this:

Modifier: Stacking Bonus->Subtype: Int Score->Additional Bonus Types: Proficiency bonus

It most likely is working, but the thing is, that👆 Modifier will increase the Base Int, not the “Set” Int. “Modifier: Set” is designed for stuff like the belts of giant strength that set that number unless the base ability score is higher than the number set. The “stacking bonus” Modifier is for stuff like the Tome of Clear Thought, Tome of Leadership and Influence, and the Tome of Understanding. So it does not apply to that “set” Ability score, it applies to the base. If the character’s  intelligence is only eight and you “set” it to 14 and then add a “Stacking proficiency bonus,” it’s only gonna show the 14 because the stacking bonus change the 8 to 10 but the 14th still higher so that’s what it’s using.