Magic pen isn't more effective against higher health, but is less effective against higher MR (which is sort of the same I guess since you would trade health for MR items).
I showed you calculations that proved flat Mpen is more effective against higher health and entirely unaffected by a persons MR unless its lower than Mpen. Do I really need to repeat myself?
EDIT: Hell, it wasnt even a calculation, it was simply logical progression from a known fact.
No, you showed calculations of a champion with high health and low MR, and one with low health and high MR. If it truly was effected by health alone then do the calculations again with both MR the same. You will find that the results aren't very satisfying.
And like I said if you buy health you are buying less MR, which means yes, in a way it is more effective against high health champions.
Okay.
dude 1 has 1000 HP 40MR = 1400 effective
dude 2 has 500 HP 40MR = 700 effective
Exact same MR. After 20 Mpen
dude 1 has 1000 HP 20 MR = 12000 effective = 200 HP reduction
dude 2 has 500 HP 20 MR = 600 effective = 100 HP reduction
Behold, proof! HP has an effect.
Now to prove that MR doesnt
dude 1 has 1000 HP 2000 MR = 21000 effective
dude 2 has 1000 HP 20 MR = 1200 effective
Exact same health, After 20 Mpen.
dude 1 has 1000 HP 1980 MR = 20800 effective = 200 reduction
dude 2 has 1000 HP no MR = 1000 effective = 200 reduction
No effect even in extreme cases.
I find these results pretty satisfying. I am assuming here, but I think you are thinking in percentage not flat health reduction, in which case stacking MR indeed makes Mpen reduce a smaller percentage of the effective health, but really, its just messing around with perentages, you arent actually reducing the amount of health Mpen takes away.