I meant to comment on The Intelligent Poker Player, Winning in tough hold em games and Limit Hold'em: winning short-handed strategies but it looks like I forgot.
I played in tough, short-handed LHE games, mostly on Bovada and some on Merge, for a short time. My "feedback" on those books has to be taken with a grain of salt because I find short-handed LHE play boring as bleep. I don't even remotely enjoy it.
But based on what little I remember, TIPP was the best of the 3 books, but the other 2 weren't particularly far behind. Even when the books disagree about the right play in a right situation they JUSTIFY their arguments, so the reader can think it through and decide for themselves which is correct.
The bottom line in short-handed play is that even though the villains aren't making the worst mistakes (i.e. playing too many starting hands, cold-calling too many preflop raises, and chasing draws they don't have odds for), they're making SOME mistakes, i.e. overdefending or underdefending their blind, c-betting too much or too little, bluffing the turn too much or not often enough etc. A good short-handed LHE book will go through the math to show what the correct frequency should be in a given situation and give you tips on how to exploit it if the villain's frequency seems wrong.
TIPP perhaps did the best job of introducing the reader to GTO - if you don't know your opponent but suspect he's a tough player, you can play GTO, and even if that doesn't help you win the MAXIMUM from your opponent, at least it helps HIM not exploit YOU while you start building up reads about his weaknesses and put together a plan to attack those.
I hope that helps, but looking back it it just seems like a blinding flash of the obvious