Realism settings

[Imp]

I would say most of the time the defender does just that, he picks the hill to defend river to stop you at etc. Only if other factors come into play like stopping you before a population centre is reached will he do otherwise & even then will try to pick the best spots.
Only if an army is near enough overrun does the attacker choose as the defender cannot reposition in time to take advantage of the terrain. He will be lucky to recover from this set back & must sacrifice units to gain time to do so once more.
Sounds rather like WW2 Blitzkrieg gave this advantage, Russia alone held on & reversed it.

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Still Dan I feel retribution coming & expect to be a couple of tanks light when I load the next turn.