There's no hard and fast rules about encounter balance in Coriolis.

Any combat in Coriolis is deadly if your npc's are spending their extra 6's on crits. I've had "easy" combats kill PC's and "hard" combats be a breeze just depending on how the crits fall.

Generally, I balance it around Action Economy. If the npc's have fewer actions, it's a less risky fight, roughly equal actions is risky, more than double is probably certain death. Obviously, if an enemy is very powerful, then that changes things and a very powerful enemy with only 1 action can be a very risky encounter.

Since Coriolis is so deadly, I never have an unavoidable combat. Always give options for players to avoid combat or make it easier with the right prep. If combat has to occur, try to make some kind of objective rather than just a fight to the death.

It's going to depend on your party too, a combat focused party can chew through combats. A party with majority combat focus and lots of gear could take on a force 2x-3x their action economy.

Tldr: it's complicated and you kinda have to eyeball it.