Basically whatever bay you call big bears spawn on the side bay or one bay left/right to the side bay.
As you may know big bears could stun you with 100% chance, and this why most players scared of them.
However tactically wise is always better to spend first turn to fight bears instead towers.
In this guide I'll show always safe starting positions to fight big bears.

Its actually pretty easy:
Big bears are very slow.
Middle bears are slow.
Yellow wolves are fast.
And small wolves are very quick.

I call it default position. It always save for any attack, but you can't hose or blast from it. Especially is good with working haste tower around.
Big bear can't attack you even hasted when you stay on it. However middle bear could hit you hasted. Hasted big bears always stand near you, and this opens them for headcrack and full turn after or any melee attack with berserk/haste2 on first turn.

This is the best position for first turn hose or blast. But its 100% save only with tech(stun) tower around.
Without haste big bears run straight to you, just as hasted big bears on Position #1 and became open for melee attacks.

As you can see only nearest tech tower could attack me. Its save to dump second one if you fighting with incoming wolves or bears in the "turtle".