What’s E and R?
From the help page:
E-value - Controls the elitism tendency of the generation algorithm. An elitist maze has a short solution relative to the size of the maze, while a non-elitist has a solution going through a larger portion of the maze.
R-value - Controls the river tendency of the generation algorithm. A maze with a high river factor has few but long dead ends, while one with a low river factor will have many short dead ends.