If you want to know what one of these range building exercisies you can watch any of my videos where I use Combonator (There is a silver one where I explore a JTo river bluff)
And no, you do NOT use your opponent's range when calculating whether something is a bluff.
You use your range which got you to this point.
i.e. preflop you'll have your preflop range (same on flop usually as we c-bet 100% in HU pots) but the action will dictate what our current range is and the decision on the river is essentially a equilibrium calculation where we know we'll be given our opponent certain odds to call us.
Lets have a look at a river bet very simply:
Assuming a simple relationship (i.e. opponent is all in if he calls) If we are giving our opponent 6-1 to call us on the river then in order to make him indifferent to calling us we have to bluff with 14% of our range (1 in 7 bets). That means no matter what stretagy our opponent choose (call% or fold%) he cannot take advantage of us bluffing.
The correct counter-strategy for him is to fold the bottom 17% of his range.
Why 17%?
Becasue we are getting 5-1 to bluff so in order for us to not make a default profit he has to call 5/6ths of the time.
If he adopts this strategy there is no adjustment we can make in our bluffing range to take advantage of it and there's no incentive for him to change so the game is in equilibirum as both players are playing optimally. If we bluff more he takes advantage of us with his calling frequecy and if we bluff less he takes advantage with his folding range.
Now obviously poker is more complex than this but that's the basis of Equilibrium play, to reach a point where your opponent cannot take advantage of what you're doing.
