How high should the true damage conversion on new Infinity Edge be?

With the upcoming Marksmen changes, Infinity Edge will have its crit damage increase replaced by a Conqueror-esque true damage conversion on crit.

Now, how much damage should be converted into true damage? The intention behind the change being to reduce burst to squishy targets and while keeping consistent/higher damage to the more tanky targets. Now, what is a tanky target? A tanky target, at the stage when new IE is normally bought (3rd or later item is the intention), is one that has 150-200 Armor between the purchase of one to two high Armor items ( ) and generally somewhat high base Armor from being level 12+.

What amount of true damage conversion equals a 25% damage increase on a 150-200 Armor target?

For 150 Armor: 1.25 DMG x (1 - 150/250) = TDC x DMG + (1 - TDC) x DMG x (1 - 150/250) 1.25 x 0.4 = TDC + (1 - TDC) x 0.4 0.5 = TDC + 0.4 - 0.4 x TDC 0.1 = 0.6 TDC TDC = 1/6 = 16.7%

For 200 Armor: 1.25 DMG x (1 - 200/300) = TDC x DMG + (1 - TDC) x DMG x (1 - 200/300) 1.25 x 1/3 = TDC + (1 - TDC) x 1/3 5/12 = 2/3 TDC + 1/3 1/12 = 2/3 TDC TDC = 1/8 = 12.5%

So, a true damage conversion of 12.5% to 16.7% would mean that a crit deals equal damage to a target with 150 to 200 Armor between the reworked IE and live IE. So, maybe 15% would be a good compromise?

Now, this is not accounting for the increased damage from more crit chance nor for the higher AD of PBE IE, there are other threads for that: https://boards.na.leagueoflegends.com/en/c/gameplay-balance/skHjxiyq-adc-burst-vs-squishies-was-not-nerfed-on-the-pbe-and-i-have-the-math-to-prove-it https://boards.na.leagueoflegends.com/en/c/gameplay-balance/QhF62fJb-math-and-other-stuff-on-pbe-adc-changes