I have many wicking beds/ containers and I never use sand or gravel.
Here's what I do use:
Wicking soil from top to the bottom of the container and surrounding the inverted buckets I use for reservoirs.
I use strait peat below the waterline, then mix compost and peat.
I cut slits in the buckets to allow water to flow in and out while excluding soil.
I cut a horizontal slit in the side of the container as an overflow.
No landscape fabric needed.
Sand added to soil mixes is said to improve drainage.
This is kind of the opposite of wicking.
There is sandponics, which uses sand as a growing medium, but I'm pretty sure this exploits sands ability to filter water, not wick it.
Sandy soil that's low in organic matter are not noted for their ability to retain water,rather the opposit.
I am not satisfied with the
sustainability of peat but it wicking ability and price point are excellent.
I think
biochar will be a good substitute but I've not followed through on implementing it.