according to the rules the starting tile can be any of the outermost tiles of the maze, not only the corners. The outermost tiles are any of the tiles that are directly on the border of the field. The robot cannot start in the middle of the field.
1.3.3 One of the outermost tiles is the starting tile, where a robot should start and exit the run.
I hope this answers your question. Please let us know if anything else is not clear.
RoboCup Junior Rescue TC 2019