I think something like this might be a good place for the "dial".
Option 1 - "Bloodied"
This option presupposes that PCs are .005 percent-ers (or less). They are potential "heroes of destiny" amidst the common fold. The condition assumes that the first portion (50%, 75 %, what have you - further dial) of a PC's HP pool is primarily a derivation of divine intervention, luck, skill/acumen; "plot armor". The second portion (50%, 25 %, what have you - further dial) of HPs is primarily (but not fully) composed of "meat". This condition is the threshold qualifier for the PC to be susceptible to certain potent spells/effects. "The common fold" (and general monsters) being "the common fold" are afforded no such "plot armor" and therefore no such threshold qualifier. They are always susceptible to all spells/effects. HP loss for them is all "meat." Therefore, there is no "plot armor" threshold for them to overcome. A hit with a weapon attack crushes, rends, etc flesh and a hit with a fire attack sears, burns, etc flesh. This dial could afford "villains of significance" (solos, elites, what have you) the same "plot armor."
Option 2 - "You are not a special and unique snowflake"
The first rule of HPs as a derivation of divine intervention, luck, skill/acumen; "plot armor" is that you do not talk about HPs as a derivation of divine intervention, luck, skill/acumen; "plot armor". Because they are meat. I suppose. Which causes all kinds of problems but ok. There you have it. Your potency and ability to withstand attacks is a product of your level (and your accrued HPs, acumen, defenses, "stuff" that comes with level). No "otherworldly" plot protection (...except increased HPs...that represent...more meat?...while you stay 5'10" 170 lbs...I don't know...don't ask me...this is all you) afforded to any PCs or BBEGs. Gods don't care about you. You have to consider the possibility that Gods don't like you. They never wanted you. In all probability, they hate you. This isn't the worst thing that could happen to you. At least you're not a scrubby nerfherder like Luke might have been if he would have been stuck another season on the farm and never stumbled upon those droids.
Option 3 - "And now for something completely different"
Something completely different that works off of a new mechanic outside of the purview of HPs or level and doesn't interact with attributes...but is effectively the same domain - eg; you get more powerful and gain more "not plot protection" as a product of it and by proxy are able to withstand more attacks.