There is one particular command I occasionally use that has totally broken completion for files, so I've taken to just using 'ls X Y Z' to get the right completion behavior and then changing 'ls' to the right command as the last step.

Hopefully you saw one of the sibling comments: https://news.ycombinator.com/item?id=44855551

TLDR: M-/ (Alt /) will do file auto-completions regardless of the commands auto-comoletion. It is a different method, but maybe could help.