I have a question. Once you hit the tab and get a list of completion items through either completion-nvim or nvim-compe, how do you further narrow down the list

I have a question. Once you hit the tab and get a list of completion items through either completion-nvim or nvim-compe, how do you further narrow down the list? All I can do is cycle through items or match by prefix, but I want further narrowing by matching substring/regex/flex anywhere in the items à la Ivy/Helm from Emacs (or any of the so many completion systems available in Emacs).