Question about medieval 2?

I keep losing battles yet I can't spot my own weakness. I try so hard to practice and kick *** against the cpu on the hardest setting but online the engine seems to favor the opponent. I know it sounds like I'm refusing to take the blame. But I observe and observe and always the odds could favor me but the enemy still wins. I could've maneuvered so damn well, but the enemy still wins. I pick the best units yet when I envelope the enemy unit, his unit lasts until reinforced. Same scenario on me though and my units rout within 10 sec of being enveloped. I always do better in the middle of the battle but my endgame sucks. I need some tips and explanations plz.