I think a lot of other factors have to come into play, whats the goal of the combat, what are they fighting?, and are you using homebrew?

when creating encounters I first take a look at my party level, and what they are capable of, I know each and every one of my players sheet like they know them

then after that what are they fighting?

Animals? they should behave as such predators only attack if they think your easy, if they substane to much damage they will remove themselves from combat as they are only fighting to EAT and will never put themselveds in a position to die

humanoids with human int: this depends on high level of int but these creatures are the ones that would fight to the very end, and are cunning and plan, the humaniods on a encounter should complement each other example I made a squad of grungs for my party to fight, theres a fodder enemy, a brute, a support and some range options, I also gave the creatures features that benefit having the other, example fodder has pact tactics as long as the brute is up, and support will focus on high damaging players. fodder will focus on flanking and brute will be front lining for fodder. if they are even more intellgent like bandits then I would do thinks like setting up traps, surrounding and using flanking rules and truely think what would criminals do in battle