Excluding files from sub-project in main project

I have a main project /

And a sub project /frontend

When I scan for files (cmd+p using sublime keymap) from my main project, I am always seeing files from my sub project appear, even though I have excluded that directory from the directories panel.

I can get around this with a scope but I don't want to have to be selecting scope from dropdown each time I do it, or if I have selected another preset from that list. I thought excluding the directory would work: