Car seat

My baby convertible car seat that I wanted to switch him to is weird it doesn’t have slots for the shoulder straps you just lift the back up and they move up. Anyway it on the lowest setting now which he fits in but the shoulder straps start behind him like in the middle of his back. And when I put the the part up it’s just up too high and his head goes forward and looks uncomfortable. Also when I do the the padding isn’t around his head. Anyway is it supposed to be all the way down his back? It doesn’t seem right and I’m confused but when I bring it up where they’re right where is shoulders are the head part is too high. I hope that makes sense and someone can help me because I’m so confused