I suggest doing both, Originally making higher armour worked fine, until the 1.3 and 1.5 patches when CA decided to change the AI archer units reaction to armoured units. Now the archers will NOT fire on units in which there armour counters their attack rating. lol So this made the AI archers not fire on heavy units. I think its still a bug as the vanilla with the patch wouldnt fire on certain units.

The way around this atleast for me is as Monkwarrior suggest change the hit points to 2, 3 seems to be too much and 2 about right. I also suggest decreasing the hit ability from 1 to .06 or so, this allows for some REALLY long battles. SPQR is the only md since its beginning that focused on Very Long battles. This works for SPQR and should work for you.

I hope CA never releases another patch for RTW because each time they do they break something else that worked or remove a feature for us. Example would be certain BI features working in RTW, that wasnt done on purpose and if they did another patch I am sure they would remove those abilities. Loyalty, recruitable generals, Night battles, rebellion characters, etc.

Lt1956