Flamestrike
Legend
What if your players scout ahead using high stealth and perception with the intent of using ranged attacks to their advantage? Do you prevent them from doing this? And if so, in what percentage of encounters do you disallow this option?
Attack them from the sides or rear or above or below.
I was in the army and patrols do just this (scout ahead with the intent of using ranged attacks to our advantage).
Sometmes it works. Quite often it doesnt and you get bumped from the sides or rear.
From a DM perspective, if you let this one tactic work more often than not, your PCs are going to use it all the time. It gets repetitive and boring, and every PC simply spams the same skills and tactics.
Use creatures with a burrow speed, high stealth scores (in a prepared ambush site giving them advantage to stealth), terrain and environment etc.
Remember, you design the encounters to challenge the PCs. Its no different to designing those encounters comparing CR to EL. You are required to take into account the party before you that you DM for. You are supposed to design your encounters to challenge those characters.
Its a difference in DMing styles. Remember; your main gripe about the system is your players use the same tactics over and over again ('they're the most optimal'), and tend to nova encounters.
So you respond by ramping up the mathmatical difficulty of those encounters. This makes your PCs use the same tactics over and over again (because theyre the most optimal), and forces them to engage in rocket tag.
You're the cause of your own problems. You're creating what youre seeing at your table.
Take a step back and try a different approach.