This one is more tricky, because in e.g. my own case (where I have unique filenames) adding the full path will just add noise, which is likely to cause many of my two letter abbreviations to not work.
But I can probably tweak the algorithm so that parent path components are given lower priority.
Maybe use tab to toggle between path and file selection. Default to just files and when you hit tab the selector is filled with /project/relative/path/to/file.html
This would be great to open one of the 100 index.htmls in your average web project