This may be like a big DUHHHHHHHHHHHh to most of you but it was a very recent discovery to me:

To keep MAC Studio Fix foundation or other powdery/minerally foundations on your face all day, use a primer or an oil control lotion underneath. It won't gum up the foundation and you can use it on both dry and oily areas of your skin.
3b (with 3c tendencies) on modified CG