One thing to keep in mind when adding multiple layers is that you lower the overall drainage capacity of the substrate if the multiple layers means a thinner top layer of the final substrate. Water will "hang" at the bottom of each transition. Best drainage is created with a homogenous and as thick layer of substrate as possible. It's the water pressure in the substrate that drains the pores, not the layer beneath the substrate whatever that is. Thicker layer means higher water pressure.
“The shortest distance between two points is often unbearable.” C Bukowski