There's another condition. Another element above or below artist picture element should be a height-adjustable element like playing tracks or artist bio, otherwise adding it won't make artist picture element resizable.
Yeah, I found out. I even installed the portable version with 3.0 just to find out if something's wrong with my settings lol, and messed around with all of the panel settings, what a process that was. In the end I found it out myself, but you were still a massive help, because I was about to give up.
Basically, have a stack of artist picture/artist bio, and under that, track information. Use that to adjust to height of your artist picture (I made it go down all the way), and then I removed the track information element, and the artist picture height stays the same.
Honestly, this is why I said that other guy used magic to make his artist picture element look like that. I just couldn't figure it out.