I'm going to test attacks on level 9 NPCs for reference.
If you attack level 10 NPCs with level 10 compass with a hero attack under 220 you get screwed.
You need to have level 9 compass and a 150+ attack hero to do well early...
(I have level 10 compass :() And...at the same time I'm in the middle of building a much larger guide on another topic. May be a bit slow to add things. AND...trying to compute hero experience gained...there is some relationship between it and the attack, there has to be. Look at this...
http://ploader.net/files/2301d615345...4b9ac931b2.jpg
If there's a rule that draws a relationship between experience and plunder (flat, btw), then I'm sure there's a rule for the attack to experience. Lossless NPC attacks provide good evidence to study...