Well, there’s a bit of a problem with that - those URL’s will behave differently.
Imagine an index.html file like this, saved in a directory called “my-picture”:
When called as https://site/my-picture , the “asset.png” should be found in /
When called as https://site/my-picture/ or https://site/my-picture/index.html, the “asset.png” should be found in the my-picture subdirectory. Further, if you have a my-picture.html next to /my-picture/ our Pretty URL’s functionality (and that of site generators like Jekyll) will need to make those behave differently.
So it is a bit more than just “always do this thing I want with trailing slashes”.
All the practical difficulties aside, I have an open feature request to allow you to specify a specific behavior, and I’ve added this thread to the request, so we can let you know if things change.
But today, we don’t have good facilities for doing much about that.