Heizung wohin?

That’s a nice set up. Depends what you want to do there.. I personally would want the black hard plastic piece to be on top of everything so that I could clean up easily any run off from watering, etc. But depending on your set up, you could also put it just like you have in the first picture- that obviously will provide the best heat for your plants because it won’t have to go thru the other layers. Hope that helps, but whatever you do.. just feel how warm it’s getting after it’s been plugged in a few hours and make your decision from that!