[Map] How can I add wild pokémon in caves?

I've created a new cave map but I can't seem to figure out how to make wild pokémon appear by just walking inside the cave. I looked at the original Fire Red ROM and the pokémon that appear in caves are selected as grass, but when I do that to my new cave map, nothing happens. I walk for minutes and not a single pokémon appears, and no, it's not the encounter ratio because I even set it up as 100% and nothing. So what am I doing wrong?

Have a look at the behaviour bytes of the tiles you're using as the 'floor' they need to be able to have wild encounters on them- see: original game caves