command to switch to corresponding header that works when the header is in a different folder

Nice idea. I like it. Not sure how you'd implement it though?

Does 'GOTO  Anything' (Super + T) not achieve this in a more general way?

I am assuming both folders you are referring to are children of a folder in the sidebar? (If not why not?)

This works in eclipse (ctrl+tab) or xcode (^⌘[up or down]) or many other editors and is one of the most used shortcuts.