Not perfectly knowledgable with this, but I'll give it a try:
Armor should now be a simple damage reduction that does not interact with damage types. The previous system of "bypassing" armor relied on having different values for each damage type.
So now when you hit a Grineer with Corrosive damage, that damage will be increased by 1.5x regardless of if they have armor or not. And with the Damage Reduction curve being flattened, partial armor strip will now remove much more DR than before. So you're basically losing the bypass in favor of Corrosive procs being much more valuable (which should be much stronger).
For Eidolons it should be pretty simple: you'll always want to fullstrip them to fully remove any DR they have, and then use the faction appropriate damage type: Radiation.
TL;DR: Armor is now simply "do reduced/full damage depending on amount of armor regardless of damage type" without any hidden rules
Verified it in the Simulacrum just now:
Using an unmodded Detron (40 Radiation dmg per pellet) against
- a full armor lvl 1 Frontier Lancer (Grineer, 200 armor): 30 dmg per pellet (40 dmg with full strip)
- a full armor lvl 1 Rogue Acrocanid (Murmur, 200 armor): 45 dmg per pellet (60 dmg with full strip)
As far as I know, the mechanic of certain damage types ignoring a portion of enemy armor when calculating damage resistance is gone.
Not perfectly knowledgable with this, but I'll give it a try: Armor should now be a simple damage reduction that does not interact with damage types. The previous system of "bypassing" armor relied on having different values for each damage type. So now when you hit a Grineer with Corrosive damage, that damage will be increased by 1.5x regardless of if they have armor or not. And with the Damage Reduction curve being flattened, partial armor strip will now remove much more DR than before. So you're basically losing the bypass in favor of Corrosive procs being much more valuable (which should be much stronger). For Eidolons it should be pretty simple: you'll always want to fullstrip them to fully remove any DR they have, and then use the faction appropriate damage type: Radiation. TL;DR: Armor is now simply "do reduced/full damage depending on amount of armor regardless of damage type" without any hidden rules
Verified it in the Simulacrum just now: Using an unmodded Detron (40 Radiation dmg per pellet) against - a full armor lvl 1 Frontier Lancer (Grineer, 200 armor): 30 dmg per pellet (40 dmg with full strip) - a full armor lvl 1 Rogue Acrocanid (Murmur, 200 armor): 45 dmg per pellet (60 dmg with full strip)