Yep. I've tried this myself. The best tactic for banners it - Get them when you see them
In the russian manual there was some kind of scores for different areas of the game. The higher the score the harder the area was. I think that last one was 95 while Elven lands were 55. I think the banners depends on those scores. Too bad i can't find where exacly they were in the manual. Grrr