It's not a good test unless the post gets promoted. I'm willing to bet that a lot of people check the promoted posts at Main, but don't bother to check New.
Also, some people might be sufficiently in favor to upvote both posts.
I've been around for more than a couple years and had no idea there was a difference between Main and Promoted. I guess I check "new" for Main by using the side bar on the landing page but didn't pick up on the distinction.
Viliam Bur made the announcement in Main, but not everyone checks main, so I'm repeating it here.