layering implies putting the one then the other then the one then the other...
so no.
and mixing, no
putting one layer on the bottom - i did 1/3, as that is what is all over the net on growing in water only or super soil, dont know about 50%. just know what i did, and why i did it is some canadian research showing that the 1/3 measure is what the plants (depending upon genetics, but all within the range tested) use during their life. when testing the soil along the lifespan of plants raised in soil with all the same constraints, the plants typically use (at whatever rate they need), most of the provided nutes by its demise when the 1/3 amount was used. they were tested in liter pots - several different sizes. all worked best with the 1/3. purple cow was not among the tested brands, but has much the same composition as those that were tested.
so, yes to putting some in the bottom, then normal soil in the rest. i used bushdoctor, but it was very specific that any good potting soil will do.
the diagram showed the roots going to the level of the water only soil, taking the nutes, then going a bit deeper and taking those nutes... till they are gone and the plant has died. the 1/3 measure was plenty, and not high enough in the pot to restrict the normal root growth (im afraid 50% would limit the growth, because they will not grow into the hot soil, they suck the good shit out first, then go down a bit more.
if you use 100% purple cow, i would be concerned it would burn her. if only a tiny bit got jumbled into my (over 12" plant) and made it crappy with splotchy leaves and slacking growth, then i would think 100% would not be a good thing. and this effect lasted till i got her out of the soil with that little bit mixed in! it was in a 1 gal, with about 2 cups of the hot soil and the rest was potting soil.
this might not be how it works for you. i dont know anything but what i personally did and the results. well, i am a voracious reader and have resources to read scholarly articles from college libraries!