Ok. THe Building Blocks are helpful.Reduce the number of opponents. Preferably by reducing it by one normal monster of the party level per player less than 5. Alternatively, you can reduce an elite to a normal mob (half hp, reduce damage/crowd control). If you reduce an elite, do one for every missing player below 5, or if it's an elite, reduce hp and maybe the damage it does, about 20% pr missing player below 5.
The building blocks of 4e encounters are:
Normal mob 1
Add up until you get an amount that equals the amount of players you have. Make the encounter harder/easier by increasing the level of the mobs by 1-2. Rarely use mobs higher/lower in level than that, compared to the party.
I'm playing 4e.Are you running 4e or PF?
Monster building will never be an exact science. What I do (and a lot of top DMs) is reduce the hp of the monster by 10hp to 20hp on the fly when an encounter difficulty seems to be above what is stated for a party size. At that point you'll be able to take statistics for your own party of how to rebalance the encounters. Sometimes this may mean adding an extra nad sometimes this may mean not.