You won't get anything remotely close to a 20% or 50% drop rate unless you are on an old server (1-22) as has also been stated hundreds of times on the forums, nor do your casualties have any effect on medal drops. They may affect rare cash item drops, but not medals. Newer servers have a drop rate closer to 1-5%, depending on what you attack. I got all my rose medals from lv 2-3 valleys repeat conquer/abandoning, with no losses. I got all my honor medals hitting lv 1-4 NPCs every hour or less, courage through freedom from lv5s, justice/nation from lv10s. The only thing thats proven to have some effect on the drop rate is whether or not the thing has troops in it or not.