Air pockets Molding

I would design the process so the pointy stuff is facing down while cast if possible. 

Maybe you need two compositions; one has a finer aggregate or is otherwise runnier to sluice into all the details, while the other stronger mix is poured over wet? 

Another thought as a non-concrete person is that the master could be re-tooled with less pointiness, so the mold doesn't have sharp crevices. 

In my casting I always pour into the lowest part of the mold.  If you have multiple sub-lowest points, they each need their pour.