Is weed barrier needed for indoor wicking bed

I m starting my own mini size wicking bed and I wonder how necessary is to place the weed barrier or any fabrics at all.

My believe is that if I lay down a 2 portions of gravel/sand mix and fill only 1 portion of water, the wick still happens without soaking the soil on top and this section will be working as a water reservoir at the same time, in that way I don’t need another space reserved and can lay down even more soil.

Is this viable? I really would appreciate any input. Thank you!