Motor-glider pilots must manage safety margins during air-starts due to the unreliability of motor-glider engines. The decision height for air-starts depends on factors such as glider characteristics, weather conditions, and landing options. 

Pilots should consider factors like altitude, field size, and motor reliability. They should have backup plans for both successful and unsuccessful starts, and always prioritize safe landing options regardless of when or where the failure occurs.

Motor-gliders require more planning, altitude, and time than pure gliders due to the added complexity of motor operations.

This is a link to an article by Dave Nadler on How Low Can You Start Your Motor