It won't "rub" on the trailing edge at 30 degrees. It will clear it. If it didn't clear it, it would be cutting it with a light finishing cut.
Also there is no absolute need to take a final straight in cut at the end when cutting at 30 degrees or less. (for a 60 degree thread).
But if you try to cut at 31 degrees or more you will leave a stair step cut on the trailing edge, and then yes, you would definitely want to remove that with a final straight in cut.
When using angles of less than thirty degrees, the trailing edge gets a nice light finishing cut during each pass, while the leading edge does the bulk removal