Yes I wish I'd put much more aquasoil under my JBL mandano substrate. At least two inches over the whole base for me next time.I wish I'd known to use a compost mix under my sand, John Innes, clay, zeolite, etc. I have it in my small tank and the plants seem much happier. I've learnt to see aquarium keeping as more like gardening, and it feels more natural to have soil.
. The sand on top I love, but better earth below.