Optimum ratio of line width to layer thickness for overhang performance?
Cura high-lights overhangs in red if the printer would end up printing completely into thin air. 

If your overhang is angled instead of being a purely vertical-to-horizontal transition, a much thinner layer height can increase the chances that enough of the prior layer exists to support the next layer being printed. 

Basically, the thinner the layer (within reason), the greater the allowable angle of overhang that is safe to print.