the upload max file size setting is only a small part of uploading larger files.
there are other settings such as max_execution_time, max_input_time and post_max_size that can also play a roll.
If the post_max_size is set to a value larger than the upload_max_filesize, then the entire form post will be rejected by the server.
Also, the script may time out before the post can complete if the max_execution_time or max_input_time settings are not set correctly.
See the following page for details on large file uploads: