IF you want to retrieve thumbnail in size that you had set with set_post_thumbnail_size()
then call the_post_thumbnail()
without passing any arguments.
That will default to named post-thumbnail
size that that set_post_thumbnail_size()
actually creates.
Also crop for this will be determined by third argument in set_post_thumbnail_size()
(defaults to false
) and is not tied to media settings (those control entirely different sizes of image).