One thing I don't understand is the "I have to make the combat deadly in order to make it a challenge". If you find that is the case, there are likely reasons for it such as OP characters with higher than normal ability scores or magic items, players that are just really good at tactics, 5 minute work days, etc..
But why is this a problem? When calculating encounter difficulty add a level or 3 to the average party level. Ignore the multiplier for the number of monsters. Crank it up to 11. The system is designed to be on the easy side, 4 person party with a non-optimal mix of PCs, minimal or no magic items, and new players. Which totally makes sense, if new DMs followed the rules and TPKed the group every other encounter, it would be quite frustrating. Meanwhile when your average party is more powerful than that, it's easy to compensate for. Just recalibrate the numbers a bit until you get it dialed in.
But why is this a problem? When calculating encounter difficulty add a level or 3 to the average party level. Ignore the multiplier for the number of monsters. Crank it up to 11. The system is designed to be on the easy side, 4 person party with a non-optimal mix of PCs, minimal or no magic items, and new players. Which totally makes sense, if new DMs followed the rules and TPKed the group every other encounter, it would be quite frustrating. Meanwhile when your average party is more powerful than that, it's easy to compensate for. Just recalibrate the numbers a bit until you get it dialed in.