The technique isn't mysterious it's just utilizing reflective light to illuminate the negative instead of transmitted light as normal enlargers use.
Think of it as a copy camera,copying the original (in this case the paper negative) to a larger size on normal photographic enlarging paper and developed,resulting in a larger print. There is a picture of the prototype reflective enlarger and my small collapsible dark room on the" paper negative group" here on APUG.
Take a look and let me know if I can be of any further help...
Don