Make engines more tolerant to overexpansion.

Currently, engines at sea level begin taking damage when their exhaust pressure is below ~55 kPa. However, Wikipedia states this:

Slight overexpansion causes a slight reduction in efficiency, but otherwise does little harm. However, if the exit pressure is less than approximately 40% that of ambient, then "flow separation" occurs. This can cause exhaust instabilities that can cause damage to the nozzle, control difficulties of the vehicle or the engine, and in more extreme cases, destruction of the engine.

Please make engines more tolerant to overexpansion.