Generally speaking, 1 instance of a Runtime Resource = 1 license used. However, there are times when a process can consume more than 1 license. There is a document discussing license usage on the BP Portal. Unfortunately, I do not recall the name of the document since it has been several years since I read it. I recommend that you search for it on your own (it might be difficult to find), or contact BP directly via a support ticket asking your question and/or asking for the name of the relevant document.
