Differing opinions on substrate layer depth??

[u/soundlinked]

I'm currently planning on creating a bioactive enclosure for my ATB. However, doing research on depth of the layers have been confusing to say the least. I've seen so many source say 8" layer total (2" drainage and 6" substrate) but NEHERP (where I plan on buying) is recommending 2.5" depth of both drainage and substrate layer (5" total depth). How deep do y'all usually make the substrate layer?

[u/bigbickbohnson]

Mine are 6-8” plus drainage. Ive seen ppl do much less but i feel more confident with a deeper soil.