I'm in the latest wardrobe and seem to no longer be able to hide my base behind the backdrop? Has this feature been removed again or what's the new secret to accomplish this?

Moved this to Help & Questions!

It depends on what backdrop you're using. It was only fairly recently that backdrops were made to be full images with no cutout for the HA. All of the older backdrops have the HA cutout, so even if you put the base layer underneath the backdrop it will still be visible.

Examples: vs

You can drag your base down below the layers :)

You can also use an item like to hide the base.

Thank you all! I indeed had chosen an "old" one. I thought it was more recent!