I am working on honor medals now as well and have had troubles. I have been hitting 1-4 lvl NPC towns and it may just be circumstance, but when I hit these towns with Ballistas...I never got medals. It seems the more troops of mine that die the better the drop rate. I have been just using warriors now and have had better luck with drop rate. Again, maybe it is just luck or whatever, but worth a try if you are desperate.