Above the upper mind connects through various channels to God encountering Bliss, peace and stillness of mind on the path. Above the upper mind avatars (God in human form) can do their work. They work on places below God.
Spiritual Masters if you are lucky enough to find one also work through aspects of God and can provide sometimes a more direct but challenging direction.
God in his formless infinite state, I have found very difficult to meditate with. The vastness and formlessness of this place makes it impossible to grasp with no footholds or rungs on the ladder just an expanse. So I have found the Avatar of this age, Meher Baba most helpful as a point of direction and I was later guided to a perfect Master Sai Baba who is my main master.
In my experience the Avatars work at a point lower than the masters and this is the point they chose to do their main work for the masses. And through this link you can be guided further to God. Even though they work at different points they maintain a pure connection through to God.