.htaccess
won't work unless the PHP script handling the upload exists at wp-content/uploads/
(which it does not). Placing it in that folder does not have the result you may expect because it only impacts scripts located in that folder.
You might try placing .htaccess
file into /wp-admin/
which will change upload settings for all files handled inside the admin PHP scripts.
Unclear from your post where else users may be uploading files... are you using upload forms in your public-facing website? If so, you may not want to update the settings server-wide. If not, I see no big risks in making the change.