Talk:Master Yi/@comment-74.65.211.149-20120123211942/@comment-4087140-20120123213517

For the record, armor penetration is less effective against high-armor targets than low-armor targets ( being an exception).

Example: Take a champion with decently low armor (e.g. at level 18 with no items): 80.5. If you have 20 armor penetration, her effective armor would decrease to 60.5 and your total physical damage increase would be about 12.46%. Take a champion with high armor (e.g. at level 18 with +200 armor from wherever): 291. If you have 20 armor penetration, his effective armor would decrease to 21 and your total physical damage increase would be about 5.39%.

tl;dr Flat armor penetration is for obliterating squishies, not making tanks vulnerable.