Genghis
Out of interest we teach turnbacks in the Grob 109B in the Air Cadet Organisation as follows:
Full engine failure - adopt glide attitude and 60kts, then assess height, up to 500' land ahead, above 500' turn back towards airfield. If landing area ahead is unsuitable you can turnback when above 300'.
Partial engine failure - if above 400' or able to climb to 400' then turn back to fly a mini-circuit to airfield, if not position to land ahead.
Even in a motorglider it needs a lot of height to be successful. Having spent about 800hrs teaching this stuff in the circuit to cadets, the wind and lift/sink conditions on the day have a massive influence and make the biggest difference to success.