I have read How do I run a game for a larger group?, and while it gave helpful advice it is not the problem I am having.
I have 6 players and an observer. They understand they need to have their turns sorted in combat and defer their turn when they need time to think.
All take part in roleplay, while not equal I do not have any "quiet players".
The problem with a team of 6, so far only 5 have been present at a time, they are breezing through encounters that should be hard.
opening encounter was 5 bandits 25xp × 5people × 2group modifier = 250 xp encounter, a hard encounter. They killed them all before taking a single hit, while the room was also on fire making them take dex saves.
A Knight level 3 encounter was killed easily. Even a centaur went down in two rounds. I thought that it would be more challenging.
The party is all level one yet it is handily slaughtering hard encounters. They work in pairs so that two are stood next to each other on each creature giving them advantage on attack rolls (as I understand it this counts as flanking, two PC both within 5 feet of the same creature), and both clerics have AC 18 making the party tough as nails.
The numbers in the book are not giving correct encounter difficulty, so how should I adjust them for a party of 6?