Lock screen background will not change with desktop background?

Hi! So this is my first ever MacBook, and I was hoping to change the lock screen background image.

Supposedly it's supposed to match the desktop background, but it only matches the desktop when I activate the lock screen from the little apple-shaped menu in the top left. When I first boot up the computer, the lock/login screen has a default abstract background which is totally different from the desktop background.

It's petty I guess, but I can't stand that abstract image--it's an eyesore and always makes me think the display is damaged for a second when I boot up.