Is there any advantage in putting the engines on the back of the fuselage
Yes, there are.
You get the engines closer to centerline. Note that Boeing 737 was the first underwing twinjet - all previous twinjets (Caravelle, BAC 1-11, DC-9) had had tail engines (except Tu-104 in-wing twin), and all previous underwing jets (B707, DC-8, CV-880, MD-119) had been quads.
Quieter cabin
Better engine ground clearance. 737 had huge difficulties with squashed engines. There is a reason most small (business and regional) jets have tail engines.
and the tail high up above them?
Cannot see any advantages. Caravelle has a low +-tail - tailplane only just out of way of engines, and thus low enough against deep stall. Jetstar and some other business jets also have +-tails. Why is T-tail better than +-tail?