I have a group that wound up being larger than I expected for my DnD Campaign. It is Dark Sun and I am keeping things gritty and dangerous. However, since I normally have 7 players, I find that combats are much nastier than expected. When I run them I feel like some of that is my players choices, but some of a it definitely is in the encounter construction. I would like to fix the issues on my end and let them suffer their own learning curve.
My question is: As I scale up encounters from the 5 player encounter to a 7 player encounter, what should I avoid? Are there combinations or creature-type distributions that get too skewed at the 7 player mark?
Important notes: I have a range of experience in my group (very to none). All the characters are well made and the group dynamic is solid. They are still level 1 at this point, getting close to level 2.