Hi!
For me, defending the BB (always action closing-so there was lo limps pre):
against SB open : around 90%
against BTN open minraise :40-50%
2,5x :30-40%
3x: 25-30%
pot: 20-25%
When SB comes along as well, I try to select hands with concentrated Equity( like 667Tss and not T764ss). And my ranges become tighter like -5%.
against CO/MP/UTG- it depends on how wide that range is (for someone UTG RFI is 30% and for another player CO RFI is 25%...) obviously the tighter the range the tighter I'd defend (or 3bet).
Regarding no. of opponents for example against UTG open-everyone folds-I'd defend 4567ss coz it will be HU, but would fold QQT2r. If UTG opens and 2 more guys coldcalls, then I'd fold 4567ss and call QQT2r. However I'm sure that in hand rankings (which ignore playability) QQT2r is ranked much higher than 4567ss. So often when deciding whether to defend, it is a function of the situation (or the situation that will arise postflop) if I choose to defend or not. And this "what situation is going to rise" is highly dependent on the player(s) U play against. If for ex. I know that opp is mainiac who will pot-pot-pot no matter what comes, than defending TT23r is viable even HU.
Defending the SB
IMO we can't really talk about "SB defend" at micros, coz if ther was an open before, the odds u get, does not differ from the odds u would get if u sat for example on the BTN or CO. This is true especially if openraise is 3BB or pot and at PLO25 where SB is 0,4BB instead of 0,5. And u will not close the action, and u will have the worst position (hard to get value, hard to bluff correctly). That said I often interpret the situation when in SB that "I would have to pay the whole open size"-coz the difference doesn't count that much. Take this with a grain of salt of course, but I hope u guys see what I mean. So I don't defend more than 20% from SB (and even this 20% is against opponents I have a clear edge against. But same principle applies : U would like to have concetrated Equity, because it is easier to play that from OOP than like a raggedy 2 pair or weak pair+draw hands.