"Mutiiple Copies" refers to 2 or 3, 95% of the time or more.

I'm an idiot... Shoulda included a poll.

"Multiple" has always meant "more than one." Your interpretation as "more than 3" is uncommon enough that using it would cause more confusion than it'd alleviate.

One way you might get at your desired outcome in a roundabout way is to install the ESGST extension and sort the "multiple copies" page by your chance to win. Generally speaking (but not always), giveaways with lots of copies will have a higher chance to win than giveaways with fewer copies.

You can just use search parameters for that. No need for an entire section:
https://www.steamgifts.com/giveaways/search?copy_min=4

Here a list of all search parameters:
https://www.steamgifts.com/discussion/1kgzB/new-search-parameters