1. Tactical map consists of hexagons.
2. Units can be upgraded and have special abilities.
3. For example two swordsmen of the 1st rank but of 6 level can easily deal with one paladin of 4th rank but of the first level.
3. The landscape affects on units’ abilities.
4. Strategic map’s landscape affects on tactical one’s.
5. If it’s hard to kill a unit (or low down HP) you can instead scare him off (low down its morale) or just exhaust it running away in swamp (low down its stamina).
So there you have it