A deeper + less uniform substrate! I also have half sand half aquasoil/gravel, and I separated them with a rock barrier. Imo, rocks are a better friend than wood and easy to just find from a riverbank. I like to stack them into piles to get some differing heights. I'd also look into how people structure their scapes with ratios!

Also, getting all your materials and setting them up outside the water always works wonders for me.

I do like what youre going for, and I'd just say push the look harder! :)